Russia said Thursday the flagship of its Black Sea fleet was severely damaged and its crew was evacuated after a fire spark caused the ammunition to detonate as a Ukrainian official said it had targeted the cruiser with a missile attack.

Sailors had contained a fire onboard the Moskva missile cruiser, the flagship of Russia's Black Sea fleet, Russia's Defense Ministry said in a statement, adding that measures were being taken to tow it back to port.

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

The ministry, which said the blaze broke out after ammunition blew up on board, said the cruiser's main weaponry had not been damaged and that its crew had been evacuated onto other ships in the Black Sea.

"The source of the blaze on the Moskva cruiser has been contained," the ministry said in a statement, adding that the vessel remained afloat. "The explosions of ammunition have stopped."

It also said it was still trying to establish the cause of the incident.

However, later on Thursday, the ministry confirmed that the Moskva cruiser sank while being towed in a storm.

"During the towing of the Moskva cruiser to the designation port, the ship lost stability due to hull damage, sustained during the detonation of ammunition because of a fire. Amid the heavy storm, the ship sank," the ministry was quoted as saying by the state news agency, Tass.

The Ministry underscored that the crew was evacuated to nearby Black Sea Fleet ships, as was announced earlier.

The Soviet-era ship had been badly damaged by the fire, the latest setback for Russia, which has suffered a series of blows since it sent troops into Ukraine on Feb. 24 in what it called a "special military operation."

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

Russia's navy has launched cruise missiles into Ukraine from the Black Sea to support its military activities in the south of the country, where it is battling to seize control of the port of Mariupol.

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 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.

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 kilometers (440 miles).

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. Ukraine's defense ministry spokesperson said he had no information about a surrender.

Capturing the 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.

"Russian forces are increasing their activities on the southern and eastern fronts, attempting to avenge their defeats," President Volodymyr Zelenskyy 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, armored personnel carriers and helicopters. France and Germany also pledged more.

Senior U.S. officials weigh 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.

Russia will view U.S. and NATO vehicles transporting weapons on Ukrainian territory as legitimate military targets, Deputy Foreign Minister Sergei Ryabkov told the TASS news agency.

'Liberate us from what?'

Ukrainian Deputy Prime Minister Iryna Vereshchuk said nine humanitarian corridors had been agreed to be opened on Thursday to evacuate civilians, including by private car from the besieged city of Mariupol.

Other evacuation routes are from Berdyansk, Tokmak and Enerhodar, and ones in the eastern Luhansk region will operate if occupying Russian forces stop 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 marooned 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.

In the village of Lubianka northwest of Kyiv, from where Russian forces had tried and failed to subdue the capital before being driven away, 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 demilitarize 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 denounced President Joe Biden's description of Moscow's actions in Ukraine as amounting to genocide, with spokesperson Dmitry Peskov saying this was unacceptable coming from the leader of a country he said had committed crimes of its own.

An initial report by a mission of experts set up by the Organization for Security and Cooperation in Europe (OSCE) documents a "catalog of inhumanity" by Russian troops in Ukraine, according to the U.S. ambassador to the OSCE.

Russia has denied targeting civilians.

The Kyiv district police chief said 720 bodies had been found in the region around the capital from where Russian forces had retreated, with more than 200 people missing.

Sanctions hit Russian jobs

Britain announced new financial measures on separatists, and Australia imposed targeted financial sanctions on 14 Russian state-owned enterprises on Thursday. Moscow and Washington have exchanged tit-for-tat sanctions on individual lawmakers.

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 Mcdonald's, have announced their withdrawal from Russia, which will directly cause the loss of about 1 million jobs, say analysts.

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