A Nigerian army official says about 100 suspected militants have been detained during a military sweep in the oil-rich Niger Delta region.
Officials say Saturday's manhunt is part of an effort to capture hostage-taking militants and locate several kidnapping victims. It is not clear if anyone has been killed in the crackdown.
At least 15 people have been abducted in the Niger Delta this month. A total of 10 have been released.
Militants are demanding that local communities receive a larger share of oil revenues.
Rivers State officials say a German oil worker who was kidnapped by suspected militants two weeks ago in Port Harcourt was released late Friday. It is not clear a ransom was paid.
Militants are demanding that local communities receive a larger share of oil revenues.
At the start of the year, Nigeria was producing 2.5 million barrels of oil per day. But kidnappings and attacks on oil facilities have cut the country's oil production by at least 20 percent since February.
Some information for this report was provided by AFP, AP and Reuters.