Ukrainian naval drones hit two sanctioned tankers in the Black Sea as they headed to a Russian port, an official said.
The two oil tankers, identified as the Kairos and Virat, were empty and sailing to Novorossiysk, a major Russian Black Sea oil terminal, the official at the Security Service of Ukraine said.
The official said the tankers were due to load up with oil destined for foreign markets.
Naval drones could be seen speeding towards hulking tankers followed by powerful explosions that caused fires on the vessels, video footage shared by the official showed.
Reuters could not independently verify the identity of the tankers in the clips or the location and date of the footage.
"Video shows that after being hit, both tankers sustained critical damage and were effectively taken out of service. This will deal a significant blow to Russian oil transportation," the official said in a written statement.
Ukraine has been attacking Russian oil refineries for months, using long-range aerial drones to strike far behind the front lines of Moscow's full-scale war against Ukraine.
The strikes on the tankers represent a different kind of attack.
Kyiv has repeatedly called on the West to take real action against Russia's so-called "shadow fleet", which the Ukrainian government says is helping Moscow export large quantities of oil and fund its war in Ukraine despite Western sanctions.
The fleet of hundreds of often ageing, unregulated vessels came to prominence after Russia's invasion of Ukraine, bypassing Western sanctions aimed at reducing Moscow's oil revenue.
Russia says attacks threaten global security
Separately, the Caspian Pipeline Consortium, which handles more than 1 per cent of global oil, said on Saturday it halted operations after a mooring at Russia's Black Sea terminal was significantly damaged by a Ukrainian naval drone attack.
Russia said it would notify all international platforms about the attack on the CPC terminal, Russian Foreign Ministry spokesperson Maria Zakharova said on Sunday, as cited by state-run RIA news agency.
Commenting on the incident, Ms Zakharova said Ukraine's actions now posed a threat to global security.
CPC exports mainly from Kazakhstan via Russia and the Black Sea terminal. Kazakhstan called the attack unacceptable.
Kazakhstan's foreign ministry said it was protesting "over yet another deliberate attack on the critical infrastructure of the international Caspian Pipeline Consortium in the waters of the Port of Novorossiysk".
"This incident marks the third act of aggression against an exclusively civilian facility whose operation is safeguarded by norms of international law," the ministry said.
Türkiye voiced concern over the attacks, saying the incidents took place in its Exclusive Economic Zone and posed serious safety risks.
Reuters