Gunmen have boarded a Greek-owned tanker anchored near a Nigerian port, killing one crew member and taking three others hostage, officials say.
The Kalamos was attacked while it was waiting to load at Qua Iboe, an oil terminal in south-eastern Nigeria.
The pirates killed a Greek deputy captain of the ship, and took two Greeks and a Pakistani citizen hostage, according to the Greek government.
The Gulf of Guinea in West Africa is regarded as a new centre of piracy.
The International Maritime Bureau recorded 33 incidents of piracy and armed robbery in the area between January and September last year, according to the AFP news agency.
Greece’s deputy shipping minister, Thodoris Dritsas, said the “foreign and shipping ministries have taken the necessary actions for the rescue of the hostages”, in a statement quoted by the Reuters news agency.
The remaining 19 crew members are believed to be safe.
The Maltese-flagged Kalamos had travelled from China without any cargo.