Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

Russian forces are likely to attack the towns of Kramatorsk and Kostiantynivka in eastern Ukraine, the U.K. Ministry of Defense warned in an intelligence update Thursday.

The towns are both located in the Donetsk Oblast of the disputed Donbas region, where Russian troops are "striking Ukrainian forces in preparation for a renewed offensive," according to the ministry.

"Urban centres have faced repeated indiscriminate attacks from Russia throughout the conflict," the ministry said. "The towns of Kramatorsk and Kostiantynivka are likely to be Russian targets for similar levels of violence."

The railway station in Kramatorsk was the site of rocket attack that killed dozens of civilians trying to evacuate the region on April 8.

"The combination of widespread missile and artillery strikes and efforts to concentrate forces for an offensive represents a reversion to traditional Russian military doctrine," the ministry added. "However, this will require significant force levels. Ukraine's continued defence of Mariupol is currently tying down significant numbers of Russian troops and equipment."

Mariupol, a strategic port city in the Donetsk Oblast, has been under heavy Russian bombardment since the start of the invasion on Feb. 24. Strong resistance from Ukrainian troops have prevented Russian forces from taking full control of Mariupol.

At least 197 children have been killed in Ukraine since the Russian invasion began, Ukraine’s Prosecutor General’s Office said on Thursday.

Another 351 children have been injured during the invasion, the office said. The actual number of casualties was assumed to be higher, because Ukraine's official figures didn’t include “full consideration of places with active hostilities,” the office said.

Two children died after being hospitalized for injuries from a rocket attack on a train station in eastern Ukraine last Friday, according to Thursday’s update. Seven children have now died following that Russian attack, the update said.

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