A Russian naval ship has been damaged in a Ukrainian naval drone attack in the Black Sea, Ukrainian sources say.

The assault is reported to have happened near the Russian port of Novorossiysk, which is a major hub for Russian exports.

Russia's defence ministry said it had repelled a Ukrainian attack with two sea drones on its naval base there.

But Ukrainian security service sources say the Olenegorsky Gornyak was hit and suffered a serious breach.

They told the BBC a sea drone was carrying 450kg (992lb) of dynamite when it hit the ship.

Russia made no mention of any damage in its report of the incident.

A video sent to the BBC by a source with Ukraine's security service appears to show the drone approaching a ship thought to be the Olenegorsky Gornyak.

The footage shows a vessel travelling right up to the side of a ship before the feed cuts out, apparently on impact.

Another unverified video is thought to show the ship listing to one side.

Ukraine has not officially claimed responsibility for the attack.

The Novorossiysk port temporarily suspended any movement of ships following the assault, according to the Caspian Pipeline Consortium, which loads oil on to tankers at the port.

Sea drones are small, unmanned vessels which operate on or below the water's surface.