The leader of of Russia's Wagner mercenary group appeared on Sunday to ditch plans to withdraw his forces from Bakhmut in eastern Ukraine after receiving promises overnight that they would get all the arms needed to capture the devastated city.

Yevgeny Prigozhin said in a new audio message that the Kremlin has promised to resupply his Wagner Private Military Company with as much ammunition and weapons as they need.

Prigozhin said that for the first time he received a response to the situation regarding the shortage of ammunition. He said on Saturday night that the relevant companies promised to deliver everything necessary to continue the offensive in Bakhmut.

"Overnight we received a combat order, for the first time in all this time," Prigozhin said. "We have been promised as much ammunition and weapons as we need to continue further operations. We have been promised that everything needed to prevent the enemy from cutting us off (from supplies) will be deployed on the flank," he added.

In addition, Russian Army Gen. Sergei Surovikin will personally deal with issues of interaction between the Wagner PMC and the Ministry of Defense, Prigozhin said. "This is the only man with the star of an army general who knows how to fight," Prigozhin said of the Russian Defense Ministry assigning Surovikin to work alongside Wagner.

Surovikin commanded Russia's Ukraine campaign for several months before the chief of the General Staff, Army Gen. Valery Gerasimov, was given overall operational command above him.

Russia is ready to use all means at its disposal to prevent anyone from encroaching on the security of the country in response to the recent drone attacks targeting the Kremlin, Russian Deputy Foreign Minister Sergey Ryabkov said in an interview on Russia's Channel One Thursday.

Ryabkov said Washington is using its "puppets" in Kyiv to stage more and more dangerous provocations.

"I think that any reasonable person in any country will understand that the United States continues its escalatory policies and uses its subordinates in Kyiv, their puppets, to stage and carry out more and more audacious, more and more dangerous, acts of provocation," he said.

He went on to say that U.S. officials may deny any responsibility and involvement in the attacks but nobody will believe them.

"We are working to prevent relations with the U.S. from plunging into the abyss of an open armed conflict. We are already standing on the edge, on the edge of this precipice," he said.

Russia’s Wagner mercenary group said it will retreat from Bakhmut because of severe shortages in ammunition, according to Yevgeny Prigozhin, the group's leader. He said his forces would withdraw on May 10, blaming Russia’s defense ministry for the retreat.

Wagner has played a crucial role for months in the fighting for Bakhmut, sustaining huge casualties. The announcement and the suggestion of bitter infighting within Russia’s military forces signals division and disorganization just as Russia is bracing for a major Ukrainian counteroffensive.

Prigozhin said he was taking the decision in retaliation against Russia’s military leadership, which he accused of deliberately starving his troops of ammunition because they are jealous of Wagner’s success.

Prigozhin and Russia’s defense ministry have been in a one-sided public feud for months. Prigozhin claims it's now reached a breaking point, delivering a blistering attack on Russia's senior military command in the video announcing the withdrawal. He accused them of being "cowards" and of denying Russians a victory in Bakhmut because of their "petty envy."

Ukrainian military officials said they did not believe Wagner forces would retreat from Bakhmut, suggesting they believed his announcement was an attempt to excuse his failure to seize the city by May 9 as he pledged. A spokesman for Ukraine's eastern command, Sergiy Cherevatyi, said Wagner was running out of fighters, not ammunition.

-ABC News' Patrick Reevell

Ukrainian President Volodymyr Zelenskyy called for a war crimes tribunal in a surprise visit to The Hague on Thursday.

"There must be accountability for this crime. And this can only be achieved through the tribunal. ... We must transform the experience of the Nuremberg trials into new operational rules. And that is why we advocate the creation of such a tribunal. We want to continue the tradition of mandatory punishment for such crimes as a guarantee of non-repetition of such aggression," Zelenskyy said.

-ABC News' Will Gretsky

A Moscow court has sentenced one of Russia's best-known opposition leaders, whose family live in the U.S., to 25 years in prison in what is widely seen a show trial.

Vladimir Kara-Murza is the most high-profile opponent of Russian President Vladimir Putin to be jailed since Alexey Navalny.

Kara-Murza's extraordinarily harsh sentence is one of the lengthiest any opposition figure has received under Putin and illustrates how repressive Russia has become during the war in Ukraine, reverting to something much closer to the USSR where no opposition is tolerated.

Kara-Murza was convicted of treason, as well as "discrediting Russia's armed forces," a new law that effectively criminalizes criticizing the war in Ukraine. He was also convicted of belonging to a banned organization. The charges are widely seen as politically motivated.

Kara-Murza is one of Russia's best-known pro-democracy figures and a veteran critic of Putin.

Kara-Murza, who holds both British and Russian citizenship, spent many years living in the United States and his wife and children still live in Virginia. He was close to the late U.S. Sen. John McCain, who championed human rights in the former Soviet Union.

Dozens of journalists and Western diplomats attended the court hearing on Monday, including the U.S. ambassador who read out a statement condemning the sentence.

"We support Mr. Kara-Murza and every Russian citizen to have a voice in the direction of their country. Mr. Kara-Murza and countless other Russians believe in and hope for a Russia where fundamental freedoms will be upheld. And we will continue to share those hopes and work for that outcome," Amb. Lynne Tracy said.

Kara-Murza previously has survived being poisoned not once but twice. In 2015 and then again in 2017, he suffered organ failure after being exposed to an unknown toxin. Independent researchers later linked the poisoning to the same team of FSB poisoners who targeted Navalny.

He chose to return to Russia after the war began, believing it was important to continue to campaign for freedom in his country and has been an outspoken critic of the invasion.

His trial was held entirely behind closed doors, but a letter containing his closing statement to the court has been released to reporters.

"I only blame myself for one thing," Kara-Murza said in the statement. "I failed to convince enough of my compatriots and politicians in democratic countries of the danger that the current Kremlin regime poses for Russia and for the world."

"Criminals are supposed to repent of what they have done. I, on the other hand, am in prison for my political views. I also know that the day will come when the darkness over our country will dissipate.

-ABC News' Patrick Reevell