"We have done a little work and learned that the Nazis had decided to establish a submarine sabotage unit on our island of Maisky," the resistance fighter said in a video sent to Sputnik.
"British instructors had been sent there to train how to use underwater drones. We passed the coordinates of this training base to the proper place, and the Russians hit the target on February 25."
He said the explosion was very powerful and was "detonating for a long time," adding that the ammunition warehouse had been completely destroyed, and many premises of the base had been flooded.
According to the fighter, the underwater drones had been being prepared for an operation related to alleged Kiev's attack on Transnistria.
"These were to attack Russian ships in the Black Sea near Odessa and at the base in Sevastopol during an attack on Transnistria," he said.
He did not provide any information on casualties among British instructors and Ukraine's forces.
The Russian Defense Ministry said in late February that Ukraine had intensified preparations for the invasion of Moldova's breakaway region of Transnistria, which poses a threat to Russian peacekeepers, adding that the Russian military would respond to this in an adequate manner.