The BBC's Barnaby Phillips: "An alarming picture of violence and lawlessness"

Despite the deployment of government troops on Friday, many buildings in the regional capital, Warri, have been set alight and eyewitnesses say there has been constant gunfire.

One resident contacted by telephone said the situation was more violent than it had ever been.

Journalists in the region have described scenes of confusion on the roads outside Warri, as people in cars and on foot tried to leave the town.

Although there was no electricity on Sunday night, eyewitnesses said the sky was lit up because of the number of buildings ablaze.

Warri is the base of many multinational oil firms, which have now withdrawn their staff or confined them to company compounds.

BBC correspondent Barnaby Phillips says Nigeria's new president, Olusegun Obasanjo, will have to act urgently to prevent the crisis undermining the government's authority.

Successive military regimes have been unable to resolve conflicts in the delta but President Obasanjo has pledged to do his best to find a solution.

Complex dispute

The delta is oil rich, but poverty stricken

The clashes are part of a long-running and complex feud over land and local government involving two main ethnic groups - the Itsekiris and the Ijaws.

A third group, the Urhobos, also appears to have joined in the confrontation, reportedly on the side of the Ijaws.

The latest violence broke out last week after an attack by armed youths on the village of Arunton near Warri.

Following reports that up to 100 people had been killed, the authorities closed the nearby port and deployed troops.

However, despite a curfew, the security forces have been unable to quell the fighting.