A spokesman for the U.S. company did not return multiple phone calls and emails seeking comment. It was unclear whether a ransom demand or any other demands had been made.
State Department spokeswoman Marie Harf said the U.S. has been concerned by "a disturbing increase" in maritime crime, including piracy, in the area.
Asked what the U.S. would do about the incident and about the long-term piracy issue in Nigeria, she said, "At this point, we're still looking into it. ... We are concerned by this increase. We've worked and will continue to work with states on the Gulf of Guinea to help them respond effectively to maritime crime in these waters."
The U.S. defense official said the U.S. Navy was monitoring the situation and that the closest military vessel was a Dutch navy ship in the Gulf of Guinea with 90 U.S. Marines aboard as part of an Africa training mission.
In July, the international agency that monitors piracy said well-armed pirates are widening their area of operations and using new strategies in the oil-rich Gulf of Guinea. The London-based International Maritime Bureau said that while piracy is down in the rest of the world, the Gulf of Guinea has overtaken Somalia as the world's new hotspot, according to figures for the first six months of the year.
There are calls for a coalition of naval forces to patrol the strategic area, but naval forces from other countries in the Gulf of Guinea have said they don't have the same capacity as Nigeria to fight piracy.
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Associated Press writers Michelle Faul in Lagos, Nigeria; Darlene Superville, Lolita C. Baldor and Deb Riechmann in Washington; and Kevin McGill in New Orleans contributed to this report.