Two ships ablaze in the Black Sea region, leaving at least 10 crew dead, caught fire while transferring fuel midsea after one vessel was barred from using its usual port in southern Russia due to U.S. sanctions risk, two sources told Reuters.

The vessels, which caught fire on Monday, have the same names as two gas-transporting tankers, the Maestro and Venice, which were included on a U.S. sanctions advisory note last year for delivering fuel to Syria.

The U.S. Treasury note, published in November, advised that any dealings with these or other vessels involved in transporting fuel to Syria could result in sanctions.