Ukraine’s Security Service (SBU) said it carried out an underwater drone strike against a Russian submarine in Novorossiysk and that the vessel was left unable to operate.

In its statement, the SBU said the operation used “Sub Sea Baby” underwater drones to blow up the submarine. The agency said the explosion caused what it described as “critical damage” and effectively took the boat out of service. Shipping Telegraph said it could not independently verify either the claim or the video released by the service.

The report stated that a submarine of this type is valued at about $400 million. It added that, in light of current international sanctions, building a similar submarine could now cost up to $500 million. According to the SBU, this class of submarine is also referred to as a “Black Hole” because its hull is designed to absorb sound and avoid detection by sonar.

The SBU called the action a “special operation” carried out jointly by the Ukrainian navy and the SBU’s 13th main directorate of military counterintelligence. It also said that four Kalibr cruise-missile launchers, which Russia uses to strike targets in Ukraine, were on board the submarine.

Russia acknowledged that an attempt had been made to use an unmanned underwater vehicle against its forces but rejected Ukraine’s version of events. Moscow said the sabotage effort with the underwater vehicle was unsuccessful and that no ships, crews or submarines were damaged, adding that they continued their duties as usual.