The main militant group in Nigeria's troubled Niger Delta region says that seven of its fighters have been killed in a new government offensive.

In its latest statement, the Movement for the Emancipation for the Niger Delta (MEND) says three army helicopter gunships Saturday fired missiles at the militants' positions in Rivers state.  Several rebels were reported wounded.

MEND says government forces used helicopter gunships, jet fighters and more than 20 gunboats and landing craft.

A Nigerian military official, Lieutenant Colonel Sagir Musa, confirmed a military engagement with the militants, but said it was in response to a rebel attack.  There is no official word on any government casualties.

MEND promised to retaliate and it warned oil companies to move their workers out of the area.

For much of the last two years, the Niger Delta has been the scene of violent unrest, much of it focused against the region's oil industry.  Kidnappings, pipeline sabotage and other violent attacks are common.

Many of the armed groups in the region say they are fighting for a greater share of the nation's oil wealth.  The inhabitants of the Delta remain desperately poor, despite the wealth pumped out of the region every day.

Other groups have targeted foreign companies, seizing workers in exchange for ransom.