Moskva, a ship in the Russian Navy's Black Sea Fleet, has been badly damaged and its crew evacuated amid the country's ongoing invasion of Ukraine.
Russian officials claimed the damage was caused by a fire on board, while a Ukrainian official claimed it was a result of a Ukrainian missile strike.
Here is what we know about the ship and what may have happened to it.
Moskva is one of Russia's most critical warships.
It is a guided missile cruiser and the flagship of the Russian Black Sea Fleet, which operates in the Black Sea, the Sea of Azov and the Mediterranean Sea.
Russian news agencies said Moskva, which was commissioned in 1983, was armed with 16 anti-ship Vulkan cruise missiles with a range of at least 700 kilometres.
During its Soviet service, the ship was known as Slava before taking the name Moskva Russian for Moscow in 2000.
The 12,500 tonne ship usually has a crew of around 500 people.
Ukrainian authorities said Moskva was in one of the landmark early exchanges of the war in Ukraine when Ukrainian border guards told the ship to go themselves after it demanded they surrender.
Ukrainian officials initially said all 13 guards had died in the Russian attack, but Ukrainian President Volodymyr Zelenskyy later said some of them survived.
Russian officials said a fire on Moskva caused some ammunition to explode, the Interfax news agency reported.
The Moskva missile cruiser was hit with ammunition detonated. The Russian Defence Ministry said in a statement that the ship was seriously damaged.
The Ukrainian governor of the region around the Black Sea port of Odesa, Maksym Marchenko, said the Moskva had been hit by two Ukrainian-made Neptune anti-ship cruise missiles that caused serious damage. He did not provide any evidence.
He said that the missile cruiser Moskva went exactly where the border guards on Snake Island told it to go.
There are unconfirmed reports that Moskva sank after sustaining this damage.
Ukraine's defence ministry did not respond to a request for comment, and the news agency Reuters was unable to verify either side's claims.
Alessio Patalano, a professor of war and strategy at King's College in London, told CNN that losing the warship would be a huge blow for Russia.
Ships operate away from public attention and their activities are rarely the subject of news, he said.
But they are large floating pieces of national territory and when you lose one, the political and symbolic message stands out just because of it, in addition to the military loss. Moskva was the second major Russian ship to suffer serious damage.
Last month, Ukraine said it destroyed a Russian landing support ship, the Orsk, on the smaller Sea of Azov.
Russia's navy launched cruise missiles into Ukraine and its activities in the Black Sea are crucial to supporting land operations in the south of the country.
Russia said 1,026 soldiers from Ukraine's 36th Marine Brigade, including 162 officers, had surrendered in the key port city of Mariupol and that the area was fully under its control.
Ukraine's defence ministry spokesman 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, strengthen a southern land corridor and allow it to expand its occupation of eastern Ukraine.