This was CNBC's live blog tracking developments on the war in Ukraine covering May 25, 2023. See here for the latest updates. 

Russian President Vladimir Putin said Russia wants to work with other countries to achieve a fair world order, criticizing a "neocolonial system" as Russia's invasion of Ukraine continues to wreak havoc on its neighbor.

Speaking at a security meeting Wednesday, Putin said he was confident that Russia and its allies could "achieve the formation of a more equitable, multipolar world, while the ideology of exceptionalism as well as the neocolonial system, which has undergirded the exploitation of the resources of the entire world, will inevitably recede into the past."

Putin made similar comments earlier this week, slamming countries that interfere in the sovereignty of others — without any hint of irony.

F-16 fighter jets will be high on the agenda as Ukraine and its international partners meet virtually on Thursday for the latest Ukraine Defense Contact Group, a coalition of nearly 50 countries supporting Ukraine's military needs.

Ukraine has repeatedly asked its allies for F-16 fighter jets to help combat Russia's ongoing invasion. The issue has returned to the fore recently and while some allies — such as the U.S., U.K. and several European partners — are willing to train Ukrainian pilots to fly F-16s, there has been little appetite to provide them.

Zelenskyy addresses graduating class of Johns Hopkins University in moving speech about the importance of time

Ukrainian President Volodymyr Zelenskyy addressed the graduating class of Johns Hopkins University and reiterated the importance of not wasting time.

Zelenskyy, who spoke virtually to the students of Johns Hopkins University, described time as "the most valuable resource on the planet."

He said that he recently returned from the frontlines after meeting with Ukrainian fighters.

"The front in Ukraine consists of very, very different people who are fighting for freedom and independence. And these are people of all ages and among them are exactly the same folks as you are. Some of them have already passed their graduation ceremony, others are only dreaming about it. They and you will have similar hopes for life, similar expectations for life," the Ukrainian leader said.

"But there is fundamental difference, it comes down to the question of time, the time of your life is under your control. The time of life of our force on the frontline, the time of life of all Ukrainians who are forced to live through this terrible Russian aggression, unfortunately, is subject to many factors that are not all in their control," he added.

— Amanda Macias

U.S. sanctions Wagner leader in Mali, citing efforts to aid Putin's war in Ukraine

The Biden administration issued sanctions against Ivan Aleksandrovich Maslov, the head of Wagner's operations in Mali.

Yevgeniy Prigozhin, the leader of the Russian paramilitary group aiding the Kremlin's war efforts in Ukraine, is already sanctioned by the United States.

According to the Treasury Department, Wagner is possibly working to obscure its networks of acquiring weapons for the Kremlin's war in Ukraine through its connections in Mali. Treasury also adds that Maslov arranges meetings between Prigozhin and government officials across Africa.

"The Wagner Group has meddled in and destablized countries in Africa, committing widespread human rights abuses and appropriating natural resources. The Wagner Group has also been involved in Kremlin-backed combat operations around the world and is a key player in support of Putin's war in Ukraine," Treasury wrote in a release announcing the sanctions.

— Amanda Macias

Impending delivery of F-16s to Ukraine a sign that Russia is "becoming weaker," Zelenskyy says

Ukrainian President Volodymyr Zelenskyy hailed the recent decision by Western allies to equip Kyiv with F-16 fighter jets.

"The first Ukrainian F-16 will be one of the strongest signals from the world that Russia will only lose because of its own aggression, becoming weaker and more isolated," Zelenskyy said in an address, according to a release from the Ukrainian government.

"Our warriors have already proved that they can master modern weapons with efficiency that was not expected from us. I'm sure they will be just as successful with the aircraft," Zelenskyy added.

For months, Kyiv has requested modern aircraft like F-16's in order to protect its skies from Russian bombardment.

— Amanda Macias

U.S. State Department announces potential weapons sale to Ukraine worth $285 million

The U.S. State Department has approved a potential foreign military sale to Ukraine for a National Advanced Surface to Air Missile System, or NASAMS.

Raytheon's facility in Tucson, Arizona, will be the primary contractor for the defense system, which is expected to cost an estimated $285 million.

"Ukraine has an urgent need to increase its capabilities to defend against Russian missile strikes and aircraft. Acquiring and effectively deploying this capability will enhance Ukraine's ability to defend its people and protect critical national infrastructure," the State Department wrote in a release announcing the sale.

— Amanda Macias

106 Ukrainian soldiers returned in latest prisoner swap, Ukraine says

Andrii Yermak, the head of Ukrainian President Volodymyr Zelenskyy's office, said 106 Ukrainian soldiers that were captured by Russian forces when fighting near Bakhmut are on their way home.

"They fought for Bakhmut and performed a feat that prevented the enemy from advancing further into our East. Each of them is a hero of our state," Yermak said on his official Telegram channel.

"All our people will be at home. We are working on it. And each exchange brings us one step closer to this goal," Yermak added.

It was not immediately clear how many Russian soldiers were involved in the prisoner exchange.

— Amanda Macias

Sixth day with no vessels sailing under Black Sea grain deal

No vessels have departed from Ukraine's ports under the Black Sea Grain Initiative in the last six days, according to the latest figures provided by the U.N.-backed organization tracking the ships.

Last week, Ukraine said there was a backlog of more than 60 ships waiting for inspection. The country has previously blamed Russia for stalling the departure of vessels.

The Black Sea grain deal, which eased a Russian naval blockade and established a humanitarian sea corridor for agricultural exports, was extended on May 17 for two months.

The last vessel to leave under the deal carried 6,800 metric tons of wheat to Italy on May 19.

— Amanda Macias

Russia summons ambassadors over Nord Stream investigations

Russia's Foreign Ministry summoned the ambassadors of Germany, Denmark and Sweden to "strongly" protest against what it saw as a "complete lack of results" of their investigations into the causes of explosions that damaged the Nord Stream gas pipelines last September.

The ministry said in a statement that it had summoned the officials due to what Russia saw as their countries' "inability to ensure transparency investigative actions."

Germany, Denmark and Sweden launched their own investigations into what happened to the gas pipelines, which span the Baltic Sea from Russia to Germany, but said they were exchanging information. Russia has repeatedly asked for its own experts to be part of the investigations into explosions that severely damaged the pipeline. But Moscow has been rebuffed, a decision it has called "unthinkable."

Investigators in Europe believe the pipelines were sabotaged but said it is difficult to establish and confirm exactly who carried out the attacks — and whether it was a state-sponsored group or not — and no definitive conclusions have been published yet. Kyiv denied any involvement in the incidents.

On Thursday, the Russian foreign ministry again lambasted "the refusal of the authorities of the Federal Republic of Germany, Denmark and Sweden to cooperate with the Russian side in this case" and accused them of "clearly dragging out time and trying to hide the traces and true perpetrators of the crime, which, as we think, are well-known countries." 

Russia said it would continue to press the countries' authorities to "conduct an objective comprehensive investigation of sabotage on the Nord Stream 1 and Nord Stream 2 gas pipelines with the obligatory involvement of Russia."

— Holly Ellyatt

Russia's Novak expects no changes in OPEC+ strategy

The influential OPEC+ alliance, made up of OPEC producers as well as Russia and a number of other oil producing countries, is unlikely to significantly adjust its crude production strategy at its upcoming meeting of June 4, Russian Deputy Prime Minister Alexander Novak told Russian media.

He further anticipates Brent crude futures will rise above $80 per barrel by the end of the year on the higher summer demand.

The OPEC+ alliance agreed in October to reduce its output by 2 million barrels per day, with several members declaring additional voluntary cuts totalling 1.6 million barrels per day in April.

Western powers have struck against Russia's oil-reliant revenues in retaliation for Moscow's full-scale invasion of Ukraine, placing sanctions on seaborne volumes that took effect in December for crude and in February for oil products. Russia continues to sell crude in Asia, primarily to Chinese and Indian buyers.

— Ruxandra Iordache

Russian soldiers replacing Wagner mercenaries in Bakhmut, official says

Ukraine said Russian soldiers are replacing Wagner Group mercenary fighters who have begun to withdraw from Bakhmut in Donetsk in eastern Ukraine.

"In the suburbs of Bakhmut, the enemy replaced Wagner's units with army regular units. At the moment, the Wagnerites remain in the city of Bakhmut," Ukraine's Deputy Defense Minister Hanna Maliar said on Telegram Thursday.

She said Ukraine's forces still controlled the southwestern outskirts of the town but that Russian forces were trying to stop Ukraine's advances on its flanks and were "pulling up additional units to the flanks for reinforcement."

The head of the Wagner Group, Yevgeny Prigozhin, said earlier Thursday that his fighters were already starting to withdraw from Bakhmut, where they've been fighting for months. Prigozhin said the withdrawal process would take several days.

"Before June 1, most of the units are rebasing to rear camps, handing over to the military, ammunitions, positions, everything, including dry rations," he said.

— Holly Ellyatt

Russian mercenaries begin withdrawal from Bakhmut

The head of Russian private military company, the Wagner Group, said his fighters are beginning to withdraw from Bakhmut in eastern Ukraine.

Yevgeny Prigozhin said that the Wagner Group had fully captured Bakhmut in the heavily contested Donetsk region last weekend, adding that it would hand the town over to the regular Russian army units around May 25.

"PMC 'Wagner' began the withdrawal of units from Bakhmut," a message posted on Wagner Group chief Yevgeny Prigozhin's Concord Group Telegram channel said.

"We're withdrawing our units from Bakhmut today, now it's 5am, 25 May, "Prigozhin said, although NBC was unable to verify if the footage had been filmed in Bakhmut.

"Before June 1, most of the units are rebasing to rear camps, handing over to the military, ammunitions, positions, everything, including dry rations," Prigozhin added, according to an NBC translation. He said his forces would have a "new objective" after having a rest following prolonged fighting in Bakhmut.

Ukraine has denied it has lost Bakhmut, with defense officials saying their forces still control a southwestern part of the town and have made progress in their bid to take back control of the flanks of the town to the north and south.

— Holly Ellyatt

Counteroffensive not a 'single event' that has a specific start, official says

One of Ukrainian President Volodymyr Zelenskyy's close advisors said the country's forthcoming counteroffensive won't have a specific start time.

There's been much speculation as to when Ukraine's much-vaunted counteroffensive will begin, with Kyiv said to have delayed the start as it awaited more weaponry from its international allies.

Mykhaylo Podolyak tweeted Thursday that it will not be a "single event" that "will begin at a specific hour of a specific day with a solemn cutting of the red ribbon."

"These are dozens of different actions to destroy the Russian occupation forces in different directions, which have already been taking place yesterday, are taking place today and will continue tomorrow," he added.

Intensive destruction of Russian logistics is also a counteroffensive, Podolyak said.

— Holly Ellyatt

Russia detains Ukrainians for plotting attack on nuclear power station lines

Russia's internal spy agency said on Thursday it had detained two Ukrainian saboteurs plotting to blow up the power lines of two nuclear power stations to shut down the reactors and embarrass Russia on the eve of this month's Victory Day holiday.

The Federal Security Service (FSB), the main successor to the Soviet-era KGB, said that the saboteurs working for Ukrainian foreign intelligence had laid explosives on a total of 11 pylons of the Leningrad and Kalinin nuclear power stations.

"The plan of the Ukrainian special services was to prompt the shutdown of the nuclear reactors, disrupt the operation of the nuclear power plants and cause serious economic and reputation damage to the Russian Federation," the FSB said in a statement.

The attacks were due to take place on the eve of the May 9 anniversary of victory over Nazi Germany, the FSB said. It did not say when the men had been arrested.

The Leningrad station is Russia's biggest atomic power plant. It is located on Gulf of Finland close to St. Petersburg. The Kalinin nuclear power station is 350 kilometers north of Moscow.

The FSB said the saboteurs were recruited in 2022 by Ukraine's foreign intelligence service (FISU) and received special training at camps in Kyiv and the Mykolaiv region. They entered Russia via Poland and Belarus, the FSB said.

Two Russian accomplices were also detained, the FSB said. The explosives — including 36.6 kg of C-4 plastic explosives, 61 detonators and 38 timers — came via Poland, Lithuania and Belarus, the FSB said.

"The defendants have confessed to cooperating with the foreign intelligence service of Ukraine in order to prepare and commit sabotage on the territory of Russia," the FSB said.

— Reuters

Russia and Minsk cement tactical nuclear weapon deployment in Belarus

Defense officials from Russia and Belarus have taken another step toward the deployment of Russian tactical nuclear weapons, also known as non-strategic nuclear weapons, on Belarusian soil.

Russian and Belarusian defense ministers met Thursday and "documents were signed defining the procedure for keeping Russian non-strategic nuclear weapons in a special storage facility on the territory of the Republic of Belarus," Belarus' defense ministry said on Telegram.

The plan to deploy tactical nuclear weapons — shorter range nuclear weapons generally designed for battlefield use — was announced back in March.

Russia said Belarus had asked for the weapons to be placed on its territory and that the construction of a storage facility for the weapons would be completed on July 1. Russia has already stationed aircraft in Belarus capable of carrying the nuclear arms. Russia said it remains in control of the weapons and any decision to use them.

This morning, Belarus and Russia's defense ministers discussed "the military-political situation and issues of military-technical cooperation between the defense departments," the ministry said.

"Deployment of non-strategic nuclear weapons is an effective response to the aggressive policy of countries unfriendly to us," Belarus' Minister of Defense, Lieutenant-General Viktor Khrenin, commented in the post. 

"To ensure military security, including the protection of the western borders of the Union State [referring to Belarus and Russia] in the Republic of Belarus, close attention is paid to the readiness and ability of the Armed Forces to fulfil their intended tasks."

— Holly Ellyatt

F-16s on the agenda as Ukraine and allies meet virtually

F-16 fighter jets will be high on the agenda as Ukraine and its international partners meet virtually on Thursday for the latest Ukraine Defense Contact Group, a coalition of nearly 50 countries supporting Ukraine's military needs.

Ukraine has repeatedly asked its allies for F-16 fighter jets to help combat Russia's ongoing invasion. The issue has returned to the fore recently and while some allies — such as the U.S., U.K. and several European partners — are willing to train Ukrainian pilots to fly F-16s, there has been little appetite to provide them.

Ukraine's President Volodymyr Zelenskyy used his nightly address Wednesday to appeal for the jets ahead of the latest contact group meeting, saying "we are doing everything to reduce the time to the result [a decision on jets], to the appearance of new and powerful aircraft with Ukrainian pilots in the Ukrainian sky."

"It is clear that this global step will expand our defense capabilities. Because only with powerful aircraft does the air defense system become complete," he said.

Ukraine fears that allies could take a lot of time to decide on fighter jets, as they did with battle tanks earlier in the year.

"The main thing is the speed of training and supply, that is, the time that will elapse between decisions and real protection of our sky," Zelenskyy said.

— Holly Ellyatt

Putin slams 'neocolonial system' as invasion of Ukraine continues

Russian President Vladimir Putin said Russia wants to work with other countries to achieve a fair world order, criticizing a "neocolonial system" as Russia's invasion of Ukraine nears its 16th month.

Speaking at a security meeting Wednesday, Putin said he was confident that Russia and its allies could "achieve the formation of a more equitable, multipolar world, while the ideology of exceptionalism as well as the neocolonial system, which has undergirded the exploitation of the resources of the entire world, will inevitably recede into the past," according to comments reported by Russian state news agency Tass.

Putin told the meeting, which included foreign security officials, that Russia was ready to cooperate with allied countries in an effort to counteract common threats.

"We highly appreciate the fact that Russia has numerous allies and partners across diverse regions and continents. We sincerely cherish our historically strong, friendly, and genuinely trust-based ties with Asian, African and Latin American countries, and we will continue to do all we can to strengthen them."

Putin's comments come a day after he slammed countries that "interfere" in the internal affairs and sovereignty of others despite Russia's ongoing invasion of its neighbor Ukraine and repeated instances of meddling in other countries' territories and political processes in recent years.

Read more on the story here: Without a hint of irony over Ukraine, Putin rages against countries that meddle in other states

— Holly Ellyatt

Discussions are ongoing for the release of Evan Gershkovich and Paul Whelan, White House says

The White House slammed the extension of Evan Gershkovich's pre-detention in Moscow and reiterated calls for his immediate release.

"It's completely just irresponsible and unacceptable that they've decided to now extend his detention another three months here while they work through their quote, unquote, judicial process. He needs to be released. He's not a criminal. He's a journalist. We want him home," National security council spokesman John Kirby said on a call with reporters.

"We're going to continue to a seek consular access to him, which they have denied us a second visit and be continued to explore options to see what we can do to negotiate to get him released and get him home where he belongs," he said, adding that the Biden administration is also working for the release of Paul Whelan.

Whelan, a former Marine, was arrested by Russian authorities in 2018 on espionage charges. At the time he was arrested, Whelan was visiting Moscow to attend a wedding, according to his brother, David Whelan. 

Whelan was convicted in 2020 and sentenced to 16 years of hard labor in a Russian camp in the remote province of Mordovia.

— Amanda Macias

Russia says warship guarding Black Sea pipelines was attacked by Ukraine

A Russian warship stationed in the Black Sea was attacked in the early morning by multiple unmanned Ukrainian speedboats, Russia's Defence Ministry said, according to Reuters.

The ministry said in a post on Telegram that the warship Ivan Hurs was protecting the TurkStream and Blue Stream gas pipelines and "continues to fulfil its tasks," Reuters reported.

Last week Russia agreed to extend the Black Sea Grain Initiative, allowing Ukraine to safely export grain in the Black Sea.

Kyiv did not immediately respond to the report, and CNBC wasn't able to immediately verify the authenticity of the footage.

— Chris Eudaily and Russian Defense Ministry | Anadolu Agency | Getty Images

Austin and Milley to discuss latest aid for Kyiv with 50 allies during Ukraine Defense Contact Group

Secretary of Defense Lloyd Austin and Chairman of the Joint Chiefs of Staff U.S. Army Gen. Mark Milley will host a virtual meeting of the Ukraine Defense Contact Group Thursday. 

The meeting will be the 12th since the Ukraine Defense Contact group, a coalition of nearly 50 countries supporting Ukraine's military needs, was formed last April.

— Amanda Macias

U.S. distances itself from pro-Ukraine incursion into Russia that involved American equipment

The United States has sought to distance itself from an alleged cross-border raid into Russian territory by pro-Ukraine fighters who appeared to use American equipment in their attack, NBC News reported.

While much is unclear about the fighting, Moscow said Tuesday it fought off an assault in its Belgorod region conducted by saboteurs from the Ukrainian military. Ukraine has said it was carried out by Russian citizens who rose up independently, according to NBC News.

The Russian Volunteer Corps, which claims to be made up of Russians fighting on behalf of Ukraine, posted video Wednesday morning showing it was in possession of Mine-Resistant Ambush Protected, or MRAP, vehicles although it was unclear where it was filmed.

Asked about the images, U.S. officials told NBC News they were monitoring the reports and added that the U.S. has not authorized Ukraine to give the equipment to anyone else and that Ukraine has not asked for the right to do so.

— Melodie Warner

Blinken and NATO chief discuss continued support for Ukraine in phone call

NATO Secretary General Jens Stoltenberg spoke with U.S. Secretary of State Antony Blinken over the phone, according to a State Department release.

"Secretary Blinken and Secretary General Stoltenberg discussed priorities for the upcoming ministerial, including preparations for the Vilnius NATO Summit in July, continued support to Ukraine, strengthening alliance deterrence and defense, and commitment to advancing Sweden's accession process," wrote State Department spokesman Matthew Miller in a statement.

The call comes one week before an informal meeting of NATO foreign ministers in Oslo, Norway.

— Amanda Macias

Russia's leadership blames the West for creating instability and rising tensions

Russian President Vladimir Putin and Moscow's top diplomat Sergey Lavrov both blamed the West for creating global insecurity and instability.

As Russia's invasion of Ukraine continues, Putin said Wednesday that the world was becoming increasingly unstable and that "new centers of tension are emerging."

Speaking at a high-level meeting in Russia on security issues, Putin said rising instability was due to individual countries and associations trying "to preserve, retain their dominance, impose their own rules, completely ignoring the sovereignty, national interests, traditions of other states."

"All this is accompanied by a buildup of military potential, unceremonious interference in the internal affairs of other countries," he said, "as well as attempts to extract unilateral advantages from the energy and food crises provoked by a number of Western states."

Speaking at the same event, Lavrov, Russia's foreign minister, said the West wanted to inflict a strategic defeat on Russia and claimed NATO weapons for Ukraine were being spread beyond the country's borders.

"The collective West does not hide its intention to inflict a strategic defeat on us. The Kyiv regime is being used as an anti-Russian battering ram, which is being pumped up with NATO weapons. At the same time, part of the Western supplies — and an increasing part — are spreading uncontrollably around the world," he said, according to a Tass news agency report.

Russia invaded Ukraine 15 months ago in a bid to overthrow the pro-Western government in Kyiv and regain its influence over the former Soviet republic. Western countries rallied around Ukraine to provide it with military and financial aid to help it defend itself against its neighbor.

— Holly Ellyatt

Read CNBC's previous live coverage here:

Russia says it'll react 'extremely harshly' to new border attacks; Kyiv fights back in Bakhmut