In the latest in a long-running spate of gun-point abductions, military spokesmen said Friday at least five foreign nationals were seized in at least two separate incidents.
Details remain sketchy, with officials giving conflicting information on the nationalities and even the number of people seized.
The Niger Delta abductions come hours after a prominent militia leader from the region, Mujahid Dokubo-Asari, was released for health reasons late Thursday after a year and a half in detention.
Dokubo-Asari, a diabetic, has appealed for bail before without success.
The timing of his release is widely seen as a key concession by the newly inaugurated President Umar Yar'Adua to militia groups whose attacks have cut oil company production and driven away most foreign staff.
Yar'Adua has promised to find a solution to the Delta crisis.
One of the largest militant groups, the Movement for the Emancipation of the Niger Delta, has announced it is suspending attacks to see what President Yar'Adua has to offer.
Charles Dokubo, an analyst at the Nigeria Institute of International Affairs, says the militant leader's release is not enough and the new president needs to address underdevelopment and the distribution of oil wealth if he is to calm the restive Delta.
"To release Asari without negotiating these bigger issues will not resolve anything," he said.
Oil industry analysts and oil workers say the latest abductions illustrate how taking foreign hostages has become a money making enterprise for criminal gangs operating outside the militants' control.
Earlier this month, the British Government said the Niger Delta was "unsafe" and urged all nationals to leave.
The Niger Delta, the source of all of Nigeria's vast oil reserves, is massively underdeveloped with few roads, schools or clinics. Since the end of military rule in 1999, frustrations in the region have been voiced through increasingly violent action.