The Black Sea has seen four attacks on commercial ships in a matter of days, and they now reach from Russia's coast to the waters of two NATO members.

The latest hit a tanker off Sochi, Russia's resort city. The Greek-owned Aframax tanker Rio was struck at about 8 p.m. local time Tuesday while carrying crude from Novorossiysk to Istanbul, Lloyd's List reported. It caught fire. All 23 Indian crew members were evacuated unharmed. Russia's transport ministry blamed Ukrainian unmanned sea vessels, SBS News reported. Ukraine has not directly commented, though Zelenskyy said recently that his country had launched "a response in the Black Sea."

The other three attacks hit ships far to the west. A Turkish cargo ship carrying Ukrainian corn sank just outside Romania's territorial waters, killing two people. Then drones struck two ships about 80 miles off Bulgaria's coast. One sank, and Bulgaria's maritime agency says there are no "traces" of at least 12 of its crew.

Bulgaria is weighing who did it. "Logically speaking, the result argues in favour of Russia," Prime Minister Rumen Radev said Wednesday. "But that does not mean that we can claim that the strike was carried out by Russia without having evidence." Russia's embassy in Bulgaria denied involvement. Zelenskyy blamed Russia for all three western attacks.

The sites matter. The attacks off Romania and Bulgaria were inside those countries' exclusive economic zones, waters where they hold rights to resources but not full control. Experts told SBS this marks a widening of the fight.

Both sides have hit ships since 2022. Russia has struck vessels carrying Ukrainian grain. Ukraine has attacked Russia's navy and its "shadow fleet," tankers used to move oil around sanctions.

What we know: Four commercial ships were hit in days, two sank, and crew are still missing off Bulgaria.
What we don't: Who launched the drones near Bulgaria and Romania.