The new violence follows separate incidents last week in which four youths were shot dead by police at the offices of U.S. Oil service company Wilbros and Shell was forced to shut in 100,000 barrels per day (bpd) of oil production.

Shell officials confirmed that the newspaper reports that a helicopter had been hijacked with five workers, including one expatriate, but were not immediately able to confirm reports of fresh attacks on the oil installations.

Youths of the Federated Niger Delta Ijaw Communities in the oil industry hub of Warri said they had attacked flow stations operated by Shell and Chevron Corp. to demand compensation for an alleged oil spill.

"The closure of the flow stations and seizure of helicopter... are a child's play considering our determination to ensure (Shell) pulls out of Ijaw land until her anti Ijaw policies are abrogated," papers quoted the group as saying.

In violence not directly related to oil production, four people were killed and 25 houses burnt in Warri in ethnic clashes between Urhobos and Ijaws.

Growing lawlessness in Nigeria's Niger Delta has made it increasingly difficult for Western firms to produce the oil which accounts for about 95 percent of export earnings to Africa's most populous nation.

Community leaders said Nigerian police shot dead four youths in an operation to dislodge protesters from offices belonging to U.S. Oil service company Wilbros near southeastern Port Harcourt on last Friday.

On the same day, the Dutch company declared force majeure -- meaning that it could not guarantee to meet export commitments-from its Bonny Terminal, following community disturbances at the 1,00,000 Barrels Per Day (BPD) of crude oil terminal.