KYIV - “Experimental” naval drones damaged two Russian military vessels - the Buyan mission carrier and the Pavel Derzhavin patrol boat - over the past two days, Ukrainian intelligence officials said Friday, as Kyiv continued a series of strikes against Moscow’s Black Sea Fleet.

The attacks on the Black Sea Fleet, which is based in occupied Crimea, have demonstrated Ukraine’s ability to operate in Kremlin-controlled waters but do not appear to have seriously reduced Moscow’s capabilities.

An official with Ukraine’s State Security Service, the SBU, said a joint operation with Ukraine’s navy had damaged the Buyan missile carrier on Friday in the port of Sevastopol. The Pavel Derzhavin patrol boat was hit two days earlier. The Russian submarine Alrosa came under attack on Thursday but escaped damage, the official said.

The official said that a new unmanned sea drone called a “Sea Baby” was used in the strikes. The official did not provide any further details.

“After the first [attack], Russian minesweepers and divers were unable to discover our ‘know-how,’” the official said, speaking on the condition of anonymity because of the sensitivity of the subject. “[The SBU] warns Muscovites that there is no need to go through Ukrainian waters if you want to preserve at least some remnants of your fleet.”

On Friday, a pro-Moscow military blogger, Rybar, reported that the Pavel Derzhavin was attacked in the morning as it was leaving Sevastopol, suffering damage to its propeller. A tugboat sent to evacuate that boat was also attacked.

“The ships remained afloat, but the extent of the damage is unknown,” Rybar wrote, adding that “the epicenter of the explosion was underwater” indicating “the use of fully submersible unmanned attack boats.”

The Black Sea Fleet is based in Sevastopol, located on the southern tip of Crimea, which Russian forces occupied and illegally annexed in 2014. Moscow has used Crimea as a springboard for its invasion of Ukraine in February 2022 and as major hub for supplies and reinforcements.

The Russia military has launched waves of deadly missile attacks on Ukrainian cities and civilian infrastructure from its sea-based missile carriers.

In recent weeks, Ukrainian forces have retaliated with their own effective campaign of missiles, self-destructing aerial drones and sea drones which have damaged or sunk several ships, Ukrainian officials said. Satellite images indicate that Moscow has relocated part of its naval forces to Novorossiysk, a Russian port on the eastern side of the Black Sea, and to other safer locations.

In September, Kyiv carried out its most successful strike, hitting the headquarters building of the Black Sea Fleet reportedly during a meeting of top commanders.

The Institute for the Study of War, a Washington D.C.-based think tank, said in a report published Sunday that while “strikes on Black Sea Fleet assets are degrading its role as a combined arms headquarters,” they “have not defeated it as a naval force.”

“Ukrainian strikes generate outsize morale shocks among Russian commanders and in the Russian information space,” ISW said.

Kamila Hrabchuk in Kyiv and Natalia Abbakumova in Riga, Latvia, contributed to this report.