Nigeria's main militant group in the Niger Delta has declared an "oil war" against forgeign-owned oil companies working in the region.
The Movement for the Emancipation of the Niger Delta (Mend) said on Sunday it had launched "hurricane Barbarossa" and destroyed flow stations and oil pipelines, killing 22 Nigerian soldiers.
Mend said it was launching the "war" after government troops attacked one of its positions a day earlier with aerial and marine forces.
Chevron confirmed one of its oil platforms was attacked by rebels on Sunday.
"There was an attack on a platform already shut down due to pipeline problems," an official said.
"There were heavy casualties on the part of the militants," Lieutenant-Colonel Sagir Musa, a military spokesman for the task force in Rivers state, said.
"We are hopeful they will give up the fight very soon."