KYIV — In another deep-strike attack against Russia, Ukraine blew up a Russian submarine docked in a secure naval base, Ukrainian counterintelligence agency Security Service of Ukraine (SBU) said Monday.

The SBU said it critically damaged the Class 636.3 submarine “Varshavyanka” (NATO reporting name: Kilo) in its home base at the port of Novorossiysk on the Black Sea.

“Ukraine’s underwater drone Sub Sea Baby attacked a Russian submarine. The explosion critically damaged the submarine and effectively disabled it. The submarine was carrying four Kalibr cruise missile launchers, which Russia uses to strike at the territory of Ukraine,” the SBU’s press service said, providing video of the blast as evidence. POLITICO could not independently verify the video.

The Russian ministry of defense so far has not issued any statements about the attack on Novorossiysk, but Russian military bloggers claim the damage was insignificant as the drone hit a nearby pier, nevertheless stating that such a close call attack is a wake-up call.

The attack, if it was as destructive as the SBU claims, will be financially costly for the Russian military. “The cost of a Varshavyanka-class submarine is about $400 million. Given the international sanctions imposed, the construction of a similar submarine could currently cost up to $500 million,” the SBU’s press service said. It’s not known if any personnel were harmed.

The attack on Novorossiysk has become the latest in Ukraine’s deep-strike campaign inside Russia against military and energy targets, now happening every day. Earlier today, the SBU hit Russia’s oil rigs in the Caspian Sea for the third time, days after Ukraine’s drones hit Russia’s oil refineries and several cargo ships of the Russian shadow fleet.

“While diplomatic processes and negotiations are underway that could bring the end of the war closer, we must not forget that Russian strikes continue every day. [Vladimir] Putin is using the brutality of the strikes as leverage in negotiations,” Ukrainian President Volodymyr Zelenskyy said in a statement at the German-Ukrainian economic forum on Monday.

“Our ability to recover from strikes, our ability to produce weapons and strike back, our ability to shoot down Russian missiles and drones — are our leverage in negotiations,” Zelenskyy added, urging partners to keep supporting Ukraine’s ability to resist Russian invasion.