On Thursday morning, the mayor of Novorossiisk in Russia's Black Sea port issued a sea-drone alert that lasted more than two full hours. Meanwhile, a group unmanned Ukrainian boats were destroyed near Crimea.

In his first message sent via Telegram, Mayor Andrei Kravchenko warned residents not to approach the shoreline of the city. In the past, Ukrainian sea drones attacked Russian ships in the vicinity of the port and disrupted traffic.

Novorossiisk, Russia's biggest Black Sea port, is a major outlet for crude and oil products exports to the south. The port also handles oil from Kazakhstan, Azerbaijan, grain, coal and fertilizers as well as food, chemicals and other cargoes.

Separately the TASS agency cited the Russian Defence Ministry as saying that 10 Ukrainian sea drones were destroyed as they approached Crimea and 33 air drones destroyed overnight over the peninsula. (Reporting and Editing by Christopher Cushing, Christian Schmollinger, and Miral Fahmy).