An official of the Ukrainian military intelligence said on Wednesday that an April fire on a Russian ship in the Baltic Sea was caused by a combined operation by his GUR agency, and a pro Kyiv Russian military unit.

GUR, the Russian intelligence agency, said that on April 7, Serpukhov, a missile ship located in Kaliningrad Region of Russia was set ablaze. The GUR intelligence agency did not claim any responsibility before.

Andriy Yusov, a spokesperson for the GUR, said that the operation was carried out in conjunction with the Freedom of Russia Legion. Russia, which launched an invasion of Ukraine on a large scale in 2022 has not made any public comments about the incident.

Ukraine conducts multiple air and navy strikes against Russian warships regularly in the Black Sea. If the damage reported to the Serpukhov was confirmed, this would be Ukraine's very first operation against Russia on the Baltic Sea.

Freedom of Russia Legion stated that the arson attack took place in conjunction with certain servicemen from Russia's Baltic Sea Fleet with whom they had been in communication since 2023.

The legion posted on Telegram that "as a consequence of the sabotage we managed to completely destroy the communication and its automation"

According to RBC-Ukraine, speaking to reporters on Wednesday in Kyiv, a former Russian Navy serviceman, who goes by Goga, said that he was able to gather classified documents from Serpukhov, before escaping.

RBC-Ukraine reported that he said: "I left the ship with classified documents, and I also left (Russia's) territory." (Reporting and writing by Tom Balmforth; editing by Alex Richardson, Mark Heinrich, and Yuliia dysa)