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

Nine humanitarian corridors are expected to reopen in eastern Ukraine on Thursday to allow civilians escape heavy fighting, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk.

She said in a statement via social media Thursday that evacuation routes were agreed upon for those traveling by private cars from besieged Mariupol in the Donetsk Oblast, as well as from Berdyansk, Tokmak and Enerhodar in the Zaporizhzhia Oblast -- all of which lead to the southeastern city of Zaporizhzhia.

In the Luhansk Oblast, Vereshchuk said routes were established from the cities of Severodonetsk, Lysychansk, Popasna, Hirske and Rubizhne, leading to the city of Bakhmut in the Donetsk Oblast.

Humanitarian corridors were not reopened the previous day because Russian forces had blocked evacuation buses in the Zaporizhzhia Oblast and violated the cease-fire in the Luhansk Oblast, according to Vereshchuk.

"All this creates such a level of danger on routes that we are forced to refrain from opening humanitarian corridors today," she said in a statement via social media Wednesday.

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