Militants in Nigeria's oil-rich Niger Delta region say they have "declared war" on the government after battling security forces guarding facilities.
The Movement for the Emancipation of the Niger Delta (Mend) said it was responding to attacks by the military.
Mend's violent campaign for a bigger part of the area's oil wealth has cut Nigeria's oil output by more than 20%.
Nigerian President Umaru Yar'adua is under pressure to crack down on the militants and make the delta safer for international oil firms.