The Russian Ministry of Defense said Thursday that the Moskva, the flagship of Russia's Black Sea fleet, sank as it was being moved to a port after a fire broke out on board.

Ukrainian officials earlier Thursday claimed their troops had fired a direct missile hit on the ship, causing major damage. But Russian authorities have only said a fire erupted on the vessel, while U.S. officials have been unable to confirm the Ukrainian missile strike.

The Russian defense ministry said the Moskva lost its stability when it was towed to a port of destination "due to damage to the hull received during the fire from the detonation of ammunition." The ship sank in stormy seas, according to the ministry.

-ABC News' James Longman

Some of the new equipment the United States is sending to Ukraine as part of an $800 million military assistance package will require a few days of in-person training that could take place in Europe, a U.S. defense official said Thursday.

The official said Ukrainian forces would need training on how to use some of the weapons being deployed to Ukraine, including 155mm howitzer cannons and short-range radar systems, the official said.

With Ukrainian troops needed in eastern Ukraine, where Russia is purportedly gearing up for a new offensive in the Donbas region, U.S. officials are looking at only pulling small numbers of Ukrainian troops over the border and training them to pass along knowledge of the new systems to fellow soldiers in their country.

The official said Gen. Tod D. Wolters, commander of the U.S. European Command and NATO's Supreme Allied Commander Europe, is working out details on how the United States will provide the training without pulling "an exorbitant number of fighters" out of Ukraine.

-ABC News' Matt Seyler

President Joe Biden confirmed Thursday that the White House is planning to send a senior official to visit Ukraine.

Before boarding Air Force One to fly to North Carolina, Biden was pressed for details by reporters but declined to elaborate.

“Well, we’re making that decision now. Thank you,” Biden said.

When a reporter asked who the White House will send to Ukraine, Biden quipped, "Ready to go?"

"Are you?" the reporter asked.

Biden responded, "Yeah," before boarding Air Force One.

Several world leaders have visited Ukraine in recent days and met with Ukrainian President Volodymyr Zelenskyy, including British Prime Minister Boris Johnson, Lithuanian President Gitanas Nauseda, Polish President Andrzej Duda, Latvian President Egils Levits and Estonian President Alar Karis.

-ABC News' Armando Garcia

White House national security advisor Jake Sullivan hinted Thursday of more sanctions coming against Russia in the "next week or two" aimed at targeting ways Moscow is evading sanctions already imposed.

“Where our focus will be over the course of the coming days is on evasion,” Sullivan said Thursday at the Economic Club of Washington. “As Russia tries to adjust to the fact that it’s under this massive economic pressure, what steps do they take to try to evade our sanctions and how do we crack down on that? And I think we'll have some announcements in the next week or two that identify targets that are trying to facilitate that evasion both inside Russia and beyond."

When Sullivan was asked whether sanctions will automatically be lifted if a negotiated peace deal between Russia and Ukraine is worked out, he appeared cautious with his words, saying, “a lot of that depends on what the shape and scope” of the agreement is.

“A lot of it depends on what the Ukrainians, in consultation with us and the Europeans come to agree to," Sullivan said. "You know, we're not going to do a deal over the head of the Ukrainians where we give a bunch of sanctions relief to Russia. But if some measure of sanctions relief were built in to some credible diplomatic solution led by the Ukrainians, that's something that we would happily discuss."

But Sullivan said Russian oligarchs shouldn't expect to ever get back their yachts and other assets seized under sanctions that have been imposed, saying the ultimate goal is "not to give them back” once the war is over.

“The president is actively looking at how we can deal with the fact that as we seize these assets, our goal is not to give them back. Our goal is to put them to a better use than that," Sullivan said. "But I'll be careful in what I say today because there's an ongoing kind of policy process around how we end up dealing with that question. But, rest assured, that the goal is not just to sit on them for a while."

-ABC News' Justin Gomez

Jalina Porter, the State Department's deputy spokesperson, is responding to the Russian attack at a Ukraine train station that killed at least 50, saying, "We can no longer be surprised by the Kremlin's repugnant disregard for human life."

Five children were among those killed when Russian rockets struck the station in Kramatorsk in Donetsk Oblast on Friday morning, according to Ukraine's state-owned railway company. At least 100 people were injured, according to Donetsk Oblast Gov. Pavlo Kyrylenko.

Russia has denied involvement in the attack, which occurred as "thousands" of civilians fleeing the Russian invasion were at the train station waiting to be taken to "safer regions of Ukraine," according to Kyrylenko.

"Civilians are killed when they stay in their homes, and they're killed when they try to leave," Porter said. "Actions like these demonstrate why Russia did not belong on the U.N. Human Rights Council, and they also reinforce the U.S. assessment that members of Russian forces are committing war crimes in Ukraine."

Porter declined to say if the department considers the train station attack a war crime, saying, "Assessing individual criminal liability in specific cases is the responsibility of courts, as well as other investigatory bodies. But as the secretary, Secretary [of State Antony] Blinken, has said, 'Those responsible for war crimes and other atrocities committed in Ukraine will be held to account.'"

-ABC News' Conor Finnegan