ISTANBUL, Aug. 29 -- The rescue mission was already underway when the second drone arrived.

A Turkish vessel, the L Kocatepe, had moved into position in the Black Sea to render assistance to the cargo ship Bordo Mavi, already struck by a drone, when it came under attack itself, according to reports circulating Thursday. The extent of damage to both ships and the condition of crew members aboard each vessel were not confirmed by Thursday evening, with no official figures released.

No government or armed group claimed responsibility for either strike.

What made the L Kocatepe attack difficult to characterize as a stray or incidental hit is the sequence. The Bordo Mavi was already stricken and in distress when the rescue vessel arrived. A...