Agip has not yet commented on the claims but a local military spokesman said that details of the attack remained sketchy.

However, he denied the militants' claims to have disarmed seven soldiers.

Violence in the Niger Delta region has severely cut production in Nigeria - one of the world's main oil exporters.

The Movement for the Emancipation of the Niger Delta (Mend) has rejected the government's offer of an amnesty.

The militant group has warned all foreign oil workers to leave the area.

Mend says its latest attack took place in Nembe creek in Bayelsa State on a pipeline supplying crude oil to Agip's Brass exports terminal.

"Our fighters encountered a military gunboat and all the soldiers numbering seven were dispossessed of their weapons. The gunboat was also stripped of its weapons before it was disabled by explosives," Mend said in an e-mail sent to news organisations.

The military is currently pursuing a major offensive against the militants which has caused thousands to flee their homes.