One of the most potent militant groups operating in Nigeria's oil-rich delta region, the Movement for the Emancipation of the Niger Delta, or MEND, says the Nigerian military were behind a cross-border raid that left 21 Cameroonian soldiers dead on Monday. Nigerian authorities deny the accusation. The attack took place in the Bakassi Peninsula, an oil-rich strip of territory recently ceded to Cameroon after international courts overturned neighboring Nigeria's claim to the land. Sarah Simpson has more from Lagos.

The MEND militant group is denying it played any role in a bloody cross-border raid and killing of 21 Cameroonian soldiers on Monday, pointing the finger instead at the Nigerian military.

In an e-mail issued to journalists late Wednesday, MEND says the Nigerian forces attacked Cameroonian troops "because of their perceived sympathy to our cause and their blind eye to a weapons route."

The Nigerian government has denied the accusation and blamed Nigerian militant groups for the deaths. Nigeria says that it has good relations with Cameroon.

The Cameroonian soldiers were killed in the Bakassi Peninsula, a narrow strip of oil-rich land long claimed by both Nigeria and Cameroon. But Nigeria's former President Olusegun Obasanjo agreed to hand-over the land to Cameroon in 2006, after the intervention of international courts. The ongoing hand-over process is scheduled to be completed next year.

Bakassi lies east of Nigeria's volatile Niger Delta where a group of armed gangs, including MEND, regularly attack oil facilities and take oil workers hostage for ransom. Such activities have cut Nigeria's substantial oil production by close to 25 percent.

Though MEND denies any involvement in the death of the Cameroonian soldiers, they did claim responsibility for an attack on an oil facility close to the Cameroonian border on the same day.

Since coming into office in May, Nigerian President Umaru Yar'Adua has repeatedly vowed to bring an end to the violence that plagues his country's oil-rich south.

But government attempts to bring militant groups into negotiations has seen allegiances splinter. In August rival gangs fought gun battles in the streets of Port Harcourt, Nigeria's southern oil-center.

On Thursday, a crude oil pipeline operated by Royal Dutch Shell was blown up, according to company officials. No one has yet claimed responsibility for the attack, which has cut output by less than 50,000 barrels per day.