The Russian Navy's guided missile cruiser Moskva sails back into a harbour after tracking NATO warships in the Black Sea, in the port of Sevastopol, Crimea November 16, 2021.
The Russian Navy's guided missile cruiser Moskva sails back into a harbour after tracking NATO warships in the Black Sea, in the port of Sevastopol, Crimea November 16, 2021. Reuters / Alexey Pavlishak

The flagship of Russia's Black Sea fleet was seriously damaged and its crew evacuated on Thursday, following an explosion on board that Ukraine said was caused by a missile strike.

The loss of the Soviet-era missile cruiser Moskva would be a blow to Russia's military - on the 50th day of the war - as it readies for a new assault in the eastern Donbas region that is likely to define the outcome of the conflict.

Russia's defence ministry said a fire on the Moskva caused ammunition to blow up, Interfax news agency reported, without saying what had caused the blaze.

Maksym Marchenko, the Ukrainian governor of the region around the Black Sea port of Odesa, said the Moskva had been hit by two Ukrainian-made Neptune anti-ship cruise missiles.

"Neptune missiles guarding the Black Sea caused very serious damage," he said in an online post.

Ukraine's defence ministry did not respond to a request for comment and Reuters was unable to verify either side's statements.

Russia's navy has launched cruise missiles into Ukraine and its activities in the Black Sea are crucial to supporting land operations in the south of the country, where it is battling to seize full control of the port of Mariupol.

Russia said on Wednesday that more than 1,000 Ukrainian marines who had been holding out in Mariupol had surrendered and that the shattered city was fully under its control. Ukrainian officials did not comment.

If it is taken, Mariupol - Ukraine's main Sea of Azov port that has been besieged and bombarded for weeks - would be the first major city to fall Russian forces since they invaded on Feb. 24.

Its capture would allow Russia to reinforce a land corridor between separatist-held eastern areas and the Crimea region it seized and annexed in 2014, and free up forces for a wider assault in the south and east.

"Russian forces are increasing their activities on the southern and eastern fronts, attempting to avenge their defeats," Ukrainian President Volodymyr Zelenskiy said in a Wednesday night video address.

HUMANITARIAN CORRIDORS

Russian news agencies said the Moskva, commissioned in 1983, was armed with 16 anti-ship Vulkan cruise missiles with a range of at least 700 km (440 miles).

Kyiv says the Moskva featured in one of the landmark early exchanges of the war, when Ukrainian border guards on Snake Island, a small outcrop in the Black Sea, told the ship to "Go fuck yourself" after it demanded they surrender.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said nine humanitarian corridors had been agreed on for Thursday to evacuate civilians, including by private car, from Mariupol.

Other evacuation routes are from Berdiansk, Tokmak and Enerhodar, and ones in the eastern Luhansk region would operate if Russian forces stopped shelling, Vereshchuk added in a statement.

Ukraine says tens of thousands of people are believed to have been killed in Mariupol and accuses Russia of blocking aid convoys to civilians trapped there.

Mariupol's mayor, Vadym Boichenko, said Russia had brought in mobile crematoria "to get rid of evidence of war crimes" - a statement that was not possible to verify.

Moscow has blamed Ukraine for civilian deaths and accused Kyiv of denigrating Russian armed forces.

'LIBERATE US FROM WHAT?'

In the village of Lubianka northwest of Kyiv, from where Russian forces had tried and failed to subdue the capital before retreating, a message to Ukrainians had been written on the wall of a house that had been occupied by Russian troops.

"We did not want this ... forgive us," it said.

The Kremlin says it launched a "special military operation" to demilitarise and "liberate" Ukraine from nationalist extremists, a message villagers said had been repeated to them by the Russian troops.

"To liberate us from what? We're peaceful ... We're Ukrainians," Lubianka resident Viktor Shaposhnikov said.

The Kremlin has denounced U.S. President Joe Biden's description of Moscow's actions in Ukraine as amounting to genocide, with spokesman Dmitry Peskov saying this was unacceptable coming from the leader of a country he said had committed crimes of its own.

A mission of experts set up by Organization for Security and Cooperation and Europe (OSCE) nations said on Wednesday it had found evidence of war crimes and crimes against humanity by Russia in Ukraine.

Russia has denied targeting civilians and said some reports have been staged for propaganda purposes.

Andriy Nyebytov, head of the Kyiv region police, said more than 800 bodies had been found in three districts which had been occupied by Russian forces.

"We are finding terrible things: buried and hidden bodies of people who were tortured and shot, and who died as a result of mortar and artillery fire," Nyebytov said in televised comments. His statements could not immediately be verified.

Western-led sanctions have triggered the worst economic crisis in Russia since the 1991 fall of the Soviet Union, say analysts.

More than 600 companies, including McDonalds, have announced their withdrawal from Russia, which will directly cause the loss of about 1 million jobs.

Overall, 2.6 million people may fall below Russia's official poverty line this year, the World Bank estimates.