Seven crew members are missing after a drone strike set the San Marino-flagged tanker Wine Trader on fire off Romania's Black Sea coast on Thursday, the BBC and Euronews reported.

The empty chemical tanker, sailing from Tunisia to Romania, reported a fire at about 7 a.m. local time (midnight ET) about 13 nautical miles southeast of Sulina, near the mouth of the Danube, the Romanian Naval Authority said. Reports differ on whether it was inside Romania's territorial waters, which reach 12 nautical miles from the coast's baselines. Euronews reported that the ship was inside them, while Reuters reported that it was struck about a mile outside them. The Naval Authority's published statement gave only the distance, and Romania's Coast Guard placed the ship near the outer limit of the territorial sea, according to the Romanian news site G4Media. "Five of the sailors on board the Wine Trader have been rescued, a further seven people are still missing," the Naval Authority said, according to Euronews. Boats and two Black Hawk helicopters searched in rough seas with very high waves, the BBC reported.

Romania resumed the search on Friday, Reuters reported in a story posted at about 5:30 a.m. ET. A Black Hawk helicopter was to put four rescuers aboard the Wine Trader while a ship searched nearby waters, officials said, according to Reuters. Strong winds and rough seas have slowed the search, the news agency reported. In a Friday morning statement carried by AGERPRES, Romania's emergency services agency said the search had resumed and did not report finding anyone.

Romanian President Nicusor Dan said the Wine Trader and another tanker, the Yara J, had both been struck by drones, the BBC reported. The Yara J caught fire late Wednesday, but its crew put out the flames, the BBC and Euronews said. Dan said "there will surely be a reaction," Euronews reported.

Dan met NATO Secretary General Mark Rutte and Bulgarian Prime Minister Rumen Radev in Brussels on Thursday to discuss security in the Black Sea, The Guardian reported. A NATO military source said the drones came from Russia, Reuters and The Guardian reported. Moscow said two cargo ships carrying military cargo to Ukraine's Odesa port had been hit, but it did not name them, the BBC said.

The strikes follow drone attacks on Tuesday that hit two ships off Bulgaria and left 11 crew members missing, the BBC and Euronews reported. Bulgaria has said Russia was likely behind those attacks but that it cannot prove it, Euronews reported.

What we know: Drones hit two tankers near Romania's coast this week, and seven sailors from the Wine Trader are still missing.
What we don't: Exactly where the Wine Trader was hit relative to Romania's territorial waters, whether Romania or NATO will formally blame Russia, and whether the missing crew will be found.