Militant youths threatened to blow up oil facilities today in the Niger Delta, as troops battled to quell tribal warfare that has shut down about 29 percent of oil-dependent Nigeria's total output.

The Nigerian unit of ChevronTexaco said it had shut all operations in the western Niger Delta and had evacuated its staff and 1,400 residents to protect them. Royal Dutch/Shell and TotalFinaElf have already halted operations.

Dozens of civilians and soldiers have died in the violence between the Ijaw and Itsekiri tribes, which has also drawn in the army.

The Ijaws, who are leading a campaign to gain a greater share of Nigeria's oil wealth, threatened to blow up crude oil flow stations if the army continued to raze their villages.

The Ijaws and the army have clashed several times since an incident on March 13 in which the army says Ijaws killed three soldiers. The army has ordered the Ijaws to hand over those responsible.

More than 75 people have been killed since troops began fighting with Ijaw militants in the village of Okorenkoko on March 12.

Oil multinationals in the West African country -- the fifth-largest supplier of petroleum products to the United States -- have been forced to cut 650,000 barrels a day, or one-third of the country's daily exports.