The loss on Thursday of the Moskva, the flagship in Russia's Black Sea fleet, occurred as it was being towed to port in stormy weather, Russian news agencies quoted the defence ministry as saying.Â
The sinking was a fresh blow to Moscow's military campaign as it readied for new assaults in east and south Ukraine that were likely to define the conflict's outcome.
Russia's defence ministry said earlier that more than 500 crew aboard the Soviet-era missile cruiser were evacuated after ammunition exploded. It did not acknowledge an attack and said the incident was under investigation.
Ukraine said it hit the warship with a Ukrainian-made Neptune anti-ship missile. Reuters was unable to verify any of the statements, including whether the ship had sunk.
The incident came as Russia's navy continues its bombardment of Ukrainian cities on the Black Sea nearly 50 days after it launched the invasion. Residents of Odesa and Mariupol, on the adjacent Azov Sea, have been bracing for new Russian attacks.
The United States said it did not have enough information to determine whether the Moskva was hit by a missile.
"(But) certainly, the way this unfolded, it's a big blow to Russia," said national security adviser Jake Sullivan.
Russian forces have pulled back from some northern parts of Ukraine after suffering heavy losses and failing to take the capital Kyiv. Ukraine and its Western allies say Moscow is redeploying for a new offensive in the eastern Donbas region.
Russia launched its assault in part to dissuade Ukraine from joining NATO. But the invasion has pushed Finland, which shares a long border with Russia, and nearby Sweden to consider joining the US-led military alliance.
Moscow warned NATO on Thursday that if Sweden and Finland join, Russia would deploy nuclear weapons and hypersonic missiles in a Russian enclave on the Baltic Sea, in the heart of Europe.
Commenting on Russia's military setbacks, CIA Director Williams Burns said the threat of Russia potentially using nuclear weapons in Ukraine cannot be taken lightly, but that the agency has not seen much practical evidence reinforcing that concern.
Russia's navy has fired cruise missiles into Ukraine and its Black Sea activities are crucial to supporting land operations in the South and East, where it is battling to seize full control of the port of Mariupol, its main target in the Donbas, after weeks of bombardment.
Russia on Wednesday said more than 1000 Ukrainian marines from one of the units still holding out in Mariupol had surrendered. Ukrainian officials did not comment.
If taken, Mariupol would be the first major city to fall to Russian forces since they invaded, allowing Moscow to reinforce a land corridor between separatist-held eastern Donbas areas and the Crimea region it seized and annexed in 2014.
Ukraine said thousands of people were believed to have been killed in Mariupol, where efforts were under way to evacuate civilians. On Thursday, Russia's defence ministry said 815 people had been evacuated from the city over the past 24 hours. Ukraine said that figure was 289.
Ukrainian officials have long warned that Russia was massing troops for assaults in the East, including on Kharkiv, Ukraine's second-largest city.
Russia said Ukraine had carried out a helicopter attack on the Russian Bryansk region, the latest of several cross-border attacks that Moscow has said may trigger a retaliatory strike on Kyiv.
Seven people were injured in the Bryansk attack, which hit residential buildings, Russian officials said. Another Russian region, Belgorod, said a village there was attacked but that no one was wounded. Neither side's statements could be verified. Ukraine's military did not reply to requests for comment.
