Three crew members are believed to have been kidnapped from a Togolese-flagged bunker tanker off Nigeria.
A possible boarding of the 400-dwt Stelios K (built 1995) by pirates was reported last Monday, 40 nautical miles (74 km) south of Lome in Togo, after it lost contact with its owner.
The incident was confirmed as a rare hijacking two days later.
Pirates had remained on board until the weekend, but security consultancy Ambrey told TradeWinds on Monday that the situation was now over, with three seafarers abducted.
