Ukrainian underwater drones struck and disabled a Russian Kilo-class attack submarine in the Russian navy's most important remaining Black Sea base, in the first operation of its kind, Ukrainian officials said on Monday.

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

Footage published by the SBU showed a powerful explosion erupting from the water at a pier near where a submarine and other vessels were docked. Reuters confirmed the location of the video using the port's layout and piers.

Alexander Kamyshin, an advisor to President Volodymyr Zelensky, wrote on X that it was the first time in history that an underwater drone had neutralised a submarine.

Ukraine, which has practically no naval fleet left, has used sea drones and missiles to harry Russia's large naval Black Sea Fleet and dislodge it from its perch in the port city of Sevastopol on the occupied peninsula of Crimea.

The diesel-electric submarine was one of many vessels that Russia was forced to move from Crimea to Novorossiysk in southern Russia, the SBU said.

The submarine is capable of carrying at least four Kalibr-type cruise missiles, one of the workhorses of Russia's massive strikes that in recent months have inflicted serious damage to the Ukrainian power grid.

Russia did not immediately comment publicly about the attack.

'TURNING POINT'

The strike comes amid a tense period of US-brokered peace negotiations that have sparked fears among Ukrainians that they will be bullied to accept settlement terms with Russia that they see as tantamount to capitulation.

Ukraine has been trying to show it can inflict significant damage on Russia, especially after US President Donald Trump said that Zelenskiy did not "have the cards" in the negotiations.

Ukrainian navy spokesperson Dmytro Pletenchuk said the operation to hit a submarine - the most difficult target to hit - marked "another turning point" in the naval battle between Ukraine and Russia.

"This day once again upends the perception of the possibilities of naval combat in this war," he told Reuters.

It will be hard for Russia to repair the submarine as that would have to be done above water, which would mean the vessel would again be exposed to attack, he added.

Russia has now lost one of its four submarines stationed in Novorossiysk, three of which are Kalibr-carriers, Pletenchuk added.

Ukraine, which has been developing long-range drone and missile capabilities to narrow the gap with Russia's large weapons arsenal, has been stepping up strikes on Russian oil, gas, power and military targets.