Several Ukrainian government sources reported Wednesday that armed forces have struck Moskva, the flagship of Russia's Black Sea fleet.

Maksym Marchenko, governor of the region around the Ukrainian port of Odesa, claimed on Telegram that two anti-ship cruise missiles struck the cruiser in the Black Sea, causing "very serious damage."

Oleksiy Arestovych, an adviser to the Ukrainian president, and Anton Gerashchenko, an adviser to the Ukrainian Ministry of Internal Affairs, reported there was an explosion and that the cruiser is on fire.

The Russian Ministry of Defense said a fire onboard the Moskva caused a subsequent broadside munitions explosion.

"The ship received serious damage, the crew was evacuated," the ministry said, adding that an investigation is underway.

There was no mention of a missile strike in the ministry's statement, which was carried by Russia's state-run news agency TASS.

-ABC News' Fidel Pavlenko, Oleksii Pshemyskyi and Christine Theodorou

U.S. Secretary of State Antony Blinken has authorized the Pentagon to provide $800 million in new military aid to Ukraine that the White House announced earlier Wednesday.

Blinken said that though Ukrainian forces are "regaining ground," the war is "far from over," with Russia repositioning itself for renewed attacks in eastern and southern Ukraine.

"The United States, its Allies and partners must take action now to surge additional military assistance as Ukraine prepares for the next phase in the fight for its freedom and its very future," Blinken said in a statement.

The new package includes increased capabilities, such as sea drones, armored vehicles and long-range artillery, he said.

-ABC News' Conor Finnegan

The U.S. will be moving "as quickly as possible" to get the latest military aid announced Wednesday into Ukraine, Pentagon spokesman John Kirby said.

"We will literally start right away," Kirby told reporters during a briefing Wednesday.

"We're aware of the clock. And we know time is not our friend," he continued.

The weapons systems, which include 155 mm howitzer artillery, are intended to help Ukraine fight against Russia in the eastern Donbas region and met requests that came from the Ukrainians, Kirby said.

"We tailored this list specifically to meet the needs that they have asked for, with respect to what's going on in eastern Ukraine," said Kirby. "That's what's really driving this."

-ABC News' Luis Martinez

President Joe Biden on Wednesday updated Ukrainian President Volodymyr Zelenskyy on ongoing efforts the United States is making to provide Ukraine with additional military support, according to the White House.

Biden and Zelenskyy spoke by phone for nearly an hour.

The call comes as the White House is expected to announce as early as Wednesday afternoon an additional military assistance package to Ukraine that could be as much as $750 million and include a range of new military hardware.

During his latest national address, Zelenskyy said they spoke about the package, as well as "the prosecution of all Russian servicemen and commanders who committed war crimes" and international cooperation for such prosecution.

-ABC News' Molly Nagle

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