Ukraine on Monday said it carried out a historic underwater drone strike that hit and disabled a Russian missile-carrying submarine docked at a Black Sea naval base, while Russia firmly denied that the attack caused any damage to its fleet or personnel.

According to Ukraine’s Security Service (SBU), the attack targeted a diesel-electric Kilo-class submarine at the port of Novorossiysk in Russia’s southern Krasnodar region. The SBU said the strike was conducted using Ukrainian-made underwater drones known as “Sub Sea Baby”, marking what Ukraine described as the first time an underwater drone has neutralised a submarine.

The submarine was docked at Novorossiysk, a port where Russia has moved many of its Black Sea Fleet vessels in recent months. Moscow shifted these ships from Sevastopol in occupied Crimea after Ukrainian drone and missile attacks made the Crimean port increasingly unsafe.

The SBU released video footage showing a large explosion erupting from the water near a pier where a submarine and several other vessels were moored. Reuters independently verified the location of the video by matching visible features with the layout and piers of the Novorossiysk port.

Alexander Kamyshin, an adviser to Ukrainian President Volodymyr Zelenskiy, said the operation marked a major moment in military history. Writing on social media platform X, he said it was “the first time in history that an underwater drone had neutralised a submarine.”

Russia swiftly rejected Ukraine’s claims. Hours after the footage was released, Russia’s Black Sea Fleet said the attack had caused no harm. State news agencies quoted the fleet as saying: “None of the ships or submarines of the Black Sea Fleet stationed in the bay of the Novorossiysk naval base, nor their crews, were damaged as a result of the sabotage and are on duty as normal.” Russian authorities did not acknowledge any loss or operational impact and said all vessels remained fully functional.

The SBU said the targeted submarine was capable of carrying at least four Kalibr cruise missiles, which are a key component of Russia’s long-range strike capability. These missiles have been used extensively in attacks that have caused serious damage to Ukraine’s power grid in recent months.

Ukraine has almost no conventional navy remaining, but it has increasingly relied on sea drones and missiles to challenge Russia’s much larger Black Sea Fleet. These tactics have helped Kyiv push Russian naval forces farther from Ukrainian shores and disrupt Moscow’s dominance in the region.

The submarine hit in Novorossiysk was one of many vessels Russia was forced to relocate from Crimea to southern Russia, according to the SBU. Ukraine calls the strike a “turning point”. Ukrainian navy spokesperson Dmytro Pletenchuk described the operation as a major breakthrough in Ukraine’s naval campaign.

Calling submarines the hardest naval targets to strike, Pletenchuk said the attack marked “another turning point” in the war at sea. “This day once again upends the perception of the possibilities of naval combat in this war,” he said.

Pletenchuk added that repairing the submarine would be extremely difficult. Any repairs would have to be carried out above water, which would leave the vessel exposed to further Ukrainian attacks.

Before Russia issued its denial, Pletenchuk said Ukraine believed Russia had effectively lost one of the four submarines stationed in Novorossiysk, noting that three of them are capable of carrying Kalibr missiles. The reported strike comes at a tense moment as U.S.-brokered peace talks continue.

Many Ukrainians fear that they may be pressured into accepting peace terms they see as tantamount to capitulation. These concerns have grown after U.S. President Donald Trump said that President Zelenskiy “did not have the cards” in negotiations with Russia. Against this backdrop, Ukrainian officials have sought to demonstrate that Ukraine can still inflict meaningful damage on Russian military assets, despite Russia’s much larger weapons arsenal.

Ukraine has stepped up the development of long-range drones and missiles in an effort to narrow the military gap with Russia. In recent months, Kyiv has increased strikes on Russian oil, gas, power and military targets, aiming to weaken Moscow’s war effort.

While Russia insists the Novorossiysk attack caused no damage, Ukraine says the operation highlights how new underwater technology is changing the nature of naval warfare and allowing Kyiv to strike targets once thought to be out of reach.

As both sides maintain sharply opposing accounts, the incident underscores the intensifying battle for control of the Black Sea and the expanding role of drones in the war between Ukraine and Russia.