MOSCOW, April 14 (Reuters) - Russia said on Thursday the flagship of its Black Sea fleet was seriously damaged and its crew evacuated following an explosion that a Ukrainian official said was the result of a missile strike.

Russia's defence ministry said a fire on the Moskva missile cruiser caused ammunition to blow up, Interfax news agency reported.

It did not say what caused the fire but Maksym Marchenko, the Ukrainian governor of the region around the Black Sea port of Odesa, said the Moskva had been hit by two Ukrainian-made Neptune anti-ship cruise missiles.

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

Ukraine's defence ministry did not respond to a request for comment and Reuters was unable to verify either side's claims.

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 operations in the Black Sea are crucial to supporting land operations in south and east Ukraine.

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 km (440 miles).