The Briton was released two weeks later on health grounds.
The main militant groups in the region have denied responsibility for the kidnap. The US Embassy was not immediately available to comment.
There have been more than 100 kidnappings during the past year in Nigeria's southern Niger Delta region.
More than 50 people have been abducted since the beginning of the year alone.
Hostage-takings for ransom have become increasingly common in Nigeria, where most people live in poverty.
Hostages are usually released unharmed, although casualties sometimes occur during gun battles between hostage-takers and the military forces that patrol the vast region of swamps and creeks.
At least four foreigners are believed to remain in captivity.