Nigeria's army raided a militant camp in the oil-producing Niger Delta on Friday, recovering arms and ammunition in what it said was part of an offensive to flush criminals out of the creeks.

Colonel Rabe Abubakar, spokesman for the joint military taskforce (JTF) in the eastern Niger Delta, said the camp in the state of Bayelsa had belonged to criminals who were behind attacks on oil facilities, soldiers and civilians.

"What the JTF is doing today is to get rid of criminals in Bayelsa who have been terrorising, robbing, killing innocent people in the state," Abubakar said.

"The JTF attacked the camp, during which the militants suffered a lot of casualties, quite a number of arms and ammunition were recovered and their camp partially destroyed."

Such military assaults on camps have in the past provoked retaliatory attacks on army installations and oil facilities by militant groups who claim to be fighting for a fairer share of the natural wealth in the Niger Delta.

The Movement for the Emancipation of the Niger Delta (MEND), the main militant group in the region, said last month it was ending a five-month-old ceasefire but has so far yet to carry out any significant attacks.

Military action against criminals and militants has been much more common in neighbouring Rivers state, whose capital Port Harcourt is the hub of the Nigerian oil industry.

State governors in Bayelsa and Delta, the two other main states in the Niger Delta, have preferred to take a diplomatic rather than overtly military approach in recent years, but security experts say that appears to be changing.