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.

Ukraine has used long-range drones to attack Russian oil platforms as it expands its strikes on the country's energy sector.

Ukraine claimed it carried out an underwater drone strike on Dec. 15, the first such attack in maritime warfare, that critically damaged a Russian Kilo-class attack submarine at the Russian port of Novorossiysk,

Russia attacked two Ukrainian ports on Friday, damaging three Turkish-owned vessels including a ship carrying food supplies, Ukrainian officials and one ship owner said, days after Moscow threatened to cut "Ukraine off from the sea".

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.

Former Swedish Foreign Minister Tobias Billström said after the Ukraine war, Europe must be ready for further Russian aggression.