The video verified by Sky News shows how the Ropucha-class landing ship appears to be listing after it was struck off the coast of Novorossiysk in southern Russia.

A second video, filmed from onboard the unmanned sea drone itself, shows the night-time attack on the large vessel.

In the clip, the Ukrainian sea drone appears to head directly towards the ship without being fired upon.

The video feed cuts out as the drone approaches the vessel.

The footage was shared on Telegram by Ukrainian government adviser Anton Gerashchenko, who said the "special operation" was carried out by the Security Service and the navy.

He added that it left a "serious hole" in the side of the vessel, which has been named by online experts as Olenegorsky Gornyak.

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Meanwhile, a Ukrainian intelligence source said the ship "received a serious breach and currently cannot conduct its combat missions".

Russia has refuted these claims, with Novorossiysk's regional governor Veniamin Kondratyev telling the RIA news agency that no damage or casualties have been reported as a result of the attack.

The strike happened in the early hours of Friday morning, with footage shared online showing loud blasts near the port, which is a major hub for Russian exports.

Sea drones, sometimes called USVs, are small, unmanned vessels that operate on or below the water's surface.

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Over the past two weeks, Russia has carried out several attacks against Ukrainian ports in the Black Sea and along the Danube River.

The wave of strikes began after Moscow pulled out of the key Black Sea grain deal, which had enabled goods to be exported safely and provided some protection to ports.

The attacks on the Danube hubs have been carried out by Iranian-produced one-way attack uncrewed aerial vehicles, according to the UK's defence ministry, and are probably an attempt to halt trading.

"It is highly likely attempting to coerce international shipping into stopping trading via the ports," it said in its latest intelligence update.