KYIV, April 13 - Russia said on Thursday the flagship of its Black Sea fleet was seriously damaged and its crew evacuated following an explosion that a Ukrainian official said was the result of a missile strike, Reuters reported.

Russia's defense ministry said a fire on the Moskva missile cruiser caused ammunition to blow up, Interfax news agency reported.

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 defense ministry did not respond to a request for comment and Reuters was unable to verify either side's claims.

The Moskva is the second major ship known to have suffered serious damage since the start of the war. Last month Ukraine said it had destroyed a landing support ship, the Orsk, on the smaller Sea of Azov.

Russia's navy has launched cruise missiles into Ukraine and its operations in the Black Sea are crucial to supporting land operations in south and east Ukraine.

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).

Ukraine warned that Russia was ramping up efforts in the south and east as it tried to seize full control of the besieged port of Mariupol.

Russia said 1,026 soldiers from Ukraine's 36th Marine Brigade, including 162 officers, had surrendered in Mariupol and that the city was fully under its control.

Capturing its Azovstal industrial district, where the marines have been holed up, would give Russia control of Ukraine's main Sea of Azov port, reinforce a southern land corridor and expand its occupation of the country's east.

Ukraine's general staff said Russian forces were attacking Azovstal and the port, but a defense ministry spokesman said he had no information about any surrender.

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

Reuters journalists accompanying Russian-backed separatists saw flames billowing from the Azovstal area on Tuesday, a day after Ukraine's 36th Marine Brigade said its troops had run out of ammunition.

The United States said on Wednesday it would send an extra $800 million worth of military hardware to Ukraine including artillery, armoured personnel carriers and helicopters. France and Germany also pledged more.

Senior U.S. officials are weighing whether to send a top cabinet member such as Secretary of State Antony Blinken and Defense Secretary Austin Lloyd to Kyiv in a show of solidarity, a source familiar with the situation said. (rt/ez)