A Ukrainian sea drone loaded with explosives hit a Russian oil tanker with 11 crew members on board in the Black Sea in Crimea but no one was hurt in the overnight attack, according to both warring nations.
Authorities revealed that the vessel's engine room was damaged in Saturday's attack which marks the second assault within 24 hours. Another attack occurred on Friday but there were no reports of damage from Russia.
A naval drone or sea drone is a small, unmanned vessel which operates on or below the water's surface and, according to research by BBC Verify, Ukraine has used the weapon for several attacks.
Saturday's operation was also carried out as a joint effort with the Ukrainian navy and 450kg of TNT explosive had been used, the BBC reported based on information provided by a Ukrainian security service source.
The SIG tanker, loaded with fuel, was found 17 miles south of the Crimean Bridge, causing "fireworks" to be visible from afar.
Two tugs had already arrived at the scene of the attack, just south of the Kerch Strait, Russia's state-run Tass news agency reported while quoting an official from the country's regional Marine Rescue Co-ordination Centre (MRCC) as saying.
"The engine room was damaged. Not much, but it was damaged," the official said.
Russia's maritime transport agency RosMorRechFlot later said the vessel had a hole "in the area of [the] engine room near the waterline from the starboard side, presumably as a result of an attack by a sea drone".
"The ship is afloat," it added.
RosMorRechFlot also reported that lights on the Crimean Bridge were turned off and traffic halted due to warnings of an imminent attack.
Ukraine designated six Russian black sea ports as "war risk" areas, indicating it could be preparing further attacks on Moscow's territory.
Meanwhile, Ukraine's National Security and Defence Council secretary Oleksiy Danilov warned of expanding combat operations in Russia.