The attack with Ukrainian-made "Sub Sea Baby" drones hit the submarine in the port of Novorossiysk where Russia has rebased many of its Black Sea naval vessels to put them out of reach of Ukrainian strikes, the Security Service of Ukraine (SBU) said.

Ukraine’s domestic security service, the SBU, said Monday that it struck a Russian submarine in the Black Sea port of Novorossiysk, causing critical damage to the vessel and effectively disabling it.

The Russian submarine was allegedly carrying Kalibr cruise missiles, which Russia has used in devastating strikes on critical infrastructure and military targets across Ukraine. The SBU said the submarine was “put out of action” as a result of the blast. The FT could not independently verify the claim.