Ukraine used domestically produced naval drones to strike two Russian oil tankers in the Black Sea, an official from Ukraine’s security services told The Associated Press on Saturday.

Video shared by the official appeared to show naval drones racing toward the large tankers, followed by strong blasts that ignited fires on the vessels.

The vessels — Kairos and Virat — described as part of Russia’s sanctions-evading “shadow fleet,” were struck in rapid succession off Turkey’s Black Sea coast, the official said.

Naval drones are uncrewed explosive-laden speed boats packed with explosives that sail towards their targets before detonating.