A fire involving two Tanzanian-flagged commercial ships near the Kerch Strait left at least 10 sailors dead on January 21.
Ukraine's Ministry of Temporary Occupied Territories claims that the two vessels were illegally smuggling gas to Syria.
"According to the OFAC of the US Treasury, the Venice and the Maestro have been involved in illegal gas supplies to Syria since 2016," the ministry said late on January 21, citing US authorities.
Among the dead are citizens of India and Turkey.
The Kerch Strait connects the Black Sea and the Sea of Azov and has been a site of tensions between Russia and Ukraine.
In November, Russian border guards opened fire on and seized three Ukrainian navy ships as they attempted to enter the waterway. Moscow continues to hold the 24 Ukrainian servicemen involved in the incident.