(Reuters) - Ukraine's special forces said on Monday they had killed Moscow's top admiral in Crimea along with 33 other officers in last week's missile attack on the headquarters of Russia's Black Sea Fleet in the port of Sevastopol.

The Russian Defence Ministry did not immediately respond when asked by Reuters to confirm or deny that Admiral Viktor Sokolov, the commander of the Black Sea Fleet and one of Russia's most senior navy officers, had been killed.

Moscow-installed authorities in Sevastopol, however, were taking extra measures to address Ukraine's increased attacks on Crimea, a critical region providing a platform from which Russia has launched many of its air attacks on Ukraine in the 19-month-long war.

If confirmed, Sokolov's killing would be one of Kyiv's most significant strikes on Crimea, which Russia seized and annexed from Ukraine in 2014.

"After the strike on the headquarters of the Russian Black Sea Fleet, 34 officers died, including the commander of the Russian Black Sea Fleet. Another 105 occupiers were wounded. The headquarters building cannot be restored," Ukraine's special forces said on the Telegram messaging app.

It was not immediately clear how Ukraine's Special Forces counted the dead and wounded in the attack.

Reuters could not independently verify the report. Each side has at times exaggerated enemy losses in the war and says little about its own losses.

In a statement after the attack, the Russian defence ministry said one serviceman was missing, revising an earlier statement that the man had been killed. Air defences had downed five missiles, the ministry said.

Ukraine has stepped up its attacks in the Black Sea and on the Crimean Peninsula and started using missiles in addition to assault drones. Kyiv has said that destroying the Russian Black Sea fleet would significantly speed up the end of the war.

Earlier this month, Russia's defence ministry said that Ukraine attacked a Black Sea naval shipyard with 10 cruise missiles.

In a possible indication of how serious the recent Ukrainian attacks on Sevastopol have been, the Russian-installed governor of the city held a meeting on Monday to work out better defence and attack warning systems for the city.

"We understand that we have moved into a new situation that requires a systemic response," Russian agencies cited the governor, Mikhail Razvozhayev, as telling its government.

"Earlier, we and our military faced attacks from unmanned vehicles ... Now everything has changed and we must be prepared for this kind of threat."