A vessel was recently attacked off the coast of Nigeria, and the captain and chief engineer -- believed to be U.S. citizens -- were taken off the craft, a U.S. official confirmed Thursday.
The attack on the vessel -- named the C-Retriever, according to the official and UK-based security firm AKE -- happened Wednesday in the Atlantic Ocean's Gulf of Guinea, off the Nigerian coast in West Africa, AKE reported.
The ship is an oil platform support vessel owned by Edison Chouest Offshore, which is based in Louisiana.
Further details about the attack weren't immediately available.
The oil-rich Gulf of Guinea produces some 5.4 million barrels of oil a day and has been the site of increasing concern over piracy, according to London-based think tank Chatham House.
Piracy in the gulf accounted for 30% of the 1,434 reported piracy attacks in African waters between 2003 and 2011 and the pace of attacks has risen since then, Chatham House reported in March.
That's in part due, the think tank said, to aggressive anti-piracy efforts by Western navies off the coast of Somalia, on the east side of the continent.