Russia-Ukraine updates: US sanctions Russian military shipbuilder, diamond miner

Russian troops that have begun to withdraw from the ground effort against Ukraine's capital of Kyiv seem to be heading north to Belarus to regroup before rejoining the fight, the Pentagon said Thursday.

"The best assessment we have – and it's an assessment at this early stage – is that they're going to be repositioned probably into Belarus to be refit and resupplied, and used elsewhere in Ukraine," Pentagon press secretary John Kirby told reporters.

It's not clear where they might go, but the Donbas region is one candidate, Kirby said.

Roughly 20% of the Russian forces that were designated to move on Kyiv are now repositioning, several U.S. officials said.

Kirby said Russian forces that are apparently leaving the Chernobyl nuclear power plant also seem to be heading toward Belarus, though noted that "indications are not completely clear at this time."

The Pentagon assesses these troops are leaving to "refit and resupply," and not due to a health hazard or other crisis at Chernobyl, Kirby said.

-ABC News' Matthew Seyler

A humanitarian corridor will open out of the besieged city of Mariupol in southeast Ukraine on Friday, the Russian Defense Ministry said.

The corridor, leading to Zaporizhzhya, will be provided by the Russian army at 10 a.m. Moscow time, according to Mikhail Mizintsev, the head of Russia's National Defense Control Center.

The announcement comes following "personal requests" by French President Emmanuel Macron and German Chancellor Olaf Scholz, Mizintsev said in a statement.

"For this humanitarian operation to be successful, we suggest it be conducted with direct participation by representatives from the UN High Commissioner for Refugees and the [International Committee of the Red Cross]," he said.

Russia had previously announced a localized cease-fire in the bombed-out port city to allow civilians to be evacuated Thursday. About 631 residents of the bombed-out city were subsequently able to evacuate in private cars, according to a Ukrainian official. Dozens of buses reserved to drive them out failed to make it into the city, the official said.

A number of previous attempts to establish humanitarian corridors out of Mariupol have failed.

The U.S. government has intelligence that shows some Russian senior officials "likely disagreed" with Russian President Vladimir Putin's decision to invade Ukraine, a U.S. official told ABC News.

"Their disillusionment is probably amplified by the Russian military's underperformance, which includes many friendly fire casualties, including shoot-downs of Russian aircraft by Russian air defense, wide-scale missile launch failures, and stiffer than expected resistance from the Ukrainian people," the official said.

The information is based on a declassified assessment from earlier this month, a source familiar with the intelligence told ABC News.

White House Communications Director Kate Bedingfield told reporters this intelligence speaks to a “larger sense that this has been a failure for Russia."

"I think we've seen reporting that morale amongst the Russian military is low and I think that would not come as a surprise to anyone who's seen what the Russian military is, is enduring here," Bedingfield said during a press briefing Thursday afternoon.

-ABC News' Mary Bruce and Justin Gomez

About 631 residents of the bombed-out city of Mariupol in southeast Ukraine were able to evacuate on Thursday, according to a Ukrainian official.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said the residents fled the city in private vehicles after 45 buses reserved to drive them out failed to make it into the city. Vereshchuk said another 600 civilians still in Mariupol plan to try to evacuate again on Friday.

Ukrainian President Volodymyr Zelenskyy said Thursday in an address to lawmakers of Australia, the Netherlands and Belgium that more than 90% of all buildings in Mariupol have been completely destroyed by Russian strikes.

"Thousands of peaceful Mariupol residents died, people are buried just in the city, in the courtyards of high-rise buildings, or rather, what is left of the high-rise buildings," Zelenskyy said.

-ABC News' Christine Theodorou