Moscow, Aug 20 (IANS): Russian authorities have said that an explosion was reported on Saturday after debris from a shot-down drone hit the staff building of the Black Sea Fleet in Crimea's Sevastopol city.

The fleet's air defences shot down the drone, Mikhail Razvozhayev, the head of the local Russian administration in the city, said, adding that "it dropped onto the roof and burned", reports dpa news agency.

There were no casualties.

The official blamed Ukraine for the attack.

Images and videos circulating on social media, whose authenticity couldn't be independently verified, showed a cloud of smoke billowing up in the sky following an explosion.

"Keep calm and stay home for the next hour if possible," Razvozhayev wrote on Telegram, adding that there were no severe damages.

According to Sevastopol's administrative head, a drone had already hit the courtyard of the building at the end of July. There were also casualties. Ukraine has denied any involvement in the attack.

A Russian ammunition depot exploded in Crimea this week and drones were also allegedly shot down over the Crimean city of Kerch on Thursday.

Without openly claiming responsibility for the attacks, the Ukrainian leadership has said it is expecting further blasts in the future, adding that Crimea isn't a safe place.

According to Russian authorities, Moscow was forced to shoot down drones in multiple locations on the Black Sea peninsula over the past days.

Sevastopol's anti-aircraft defence was active, it hit its targets, Razvozhayev said on Friday evening, reporting that he'd heard several explosions in the city centre.

Unverified videos on social media which were said to be filmed in Yevpatoriya showed tracers of anti-aircraft fire over the city.

Drones were also allegedly shot down over the Crimean city of Kerch on Thursday.