Pirates have attacked an oil supply vessel owned by the US marine transport group Edison Chouest Offshore off the Nigerian coast and took hostage the captain and chief engineer of the ship, according to US defence officials.
A UK-based security firm, AKE, and two security sources were quoted by Reuters as saying that the two US mariners were kidnapped from the US-flagged 222ft-long vessel named C-Retriever.
According to an US official, the vessel and 11 other crew members of the ship were released and the two hostages are believed to have been taken to shore in Nigeria.
The number of pirate attacks in the region has gone up by a third in 2013, as pirates look for cargoes and crews in ships passing through the West Africa’s Gulf of Guinea.
A US defence official said the State Department and FBI were leading the American response to the incident.
White House spokesman Jay Carney said they are seeking additional information so they can contribute to the safe resolution of the situation.
"Our principal concern now is the safe return of two American citizens," Carney added.
C-Level Maritime Risks, a US-based consultancy, official Michael Frodl said that the threat from piracy is spreading even further through the waters of West Africa, and that attacks have been mounting, even as global rates of reported piracy are at their lowest since 2006.
The incident follows the recent attack on a vessel carrying construction workers in the creeks of oil producing Rivers state, in which three Nigerian soldiers were killed.