Russia’s military says the flagship of its Black Sea fleet — the guided missile cruiser Moskva — sank as it was being towed to port Thursday, forcing some 500 sailors to abandon ship. The loss of the Moskva was reported hours after Ukraine’s military claimed it had successfully attacked the warship with cruise missiles. Russia contends the ship was damaged after a fire caused ammunition onboard to explode.

This comes as The Washington Post is reporting the Russian government has formally warned the Biden administration to stop arming Ukraine, claiming it was “adding fuel” to the conflict. Russia also warned the governments of Finland and Sweden against joining NATO, saying it’s prepared to station more nuclear weapons in the Baltic Sea region in response to further NATO expansion. The threat came as CIA Director William Burns warned the U.S. should not discount the threat of Russia potentially using tactical nuclear weapons in Ukraine out of desperation.