Russia’s defence ministry has announced that Moskva, one of the country’s most essential warships, sank in stormy seas following a major fire incident on April 14.

While the Russian defence ministry claimed the explosion of ammunition on board the warship caused the loss, Ukraine said it struck the Moskva with a missile, Reuters reported.

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“The cruiser ship Moskva lost its stability when it was towed to the port because of the damage to the ship’s hull that it received during the fire from the detonation of ammunition. In stormy sea conditions, the ship sank,” the Russian defence ministry said in a statement.

Moskva was a guided missile cruiser of the Russian Navy, named after the city of Moscow. Originally built in the Soviet-era (the USSR era), the warship entered service in the early 1980s.

Moskva was the flagship of the Russian Navy that led the naval onslaught in Russia’s invasion of Ukraine. It is also the most powerful surface vessel in the region.

The estimated value of the warship is $750 million, making it the most expensive military loss recorded by Russia since the invasion started on February 24.