About 500 people have been killed during a month of escalating violence in Nigeria's oil-rich delta region.
Rival gangs involved in stealing an estimated 100,000 barrels of crude oil a day from pipelines and wellheads have stepped up attacks in the eastern Niger delta in the state of Rivers.
"This level of violence represents a serious threat to the region," said Mr George Ngwa, an Amnesty International press officer for African affairs, yesterday.
Security forces have already begun 24-hour patrols in and around the state capital and oil hub Port Harcourt after a surge of fighting last month. The gangs, which sell the oil to buy weapons, are often backed by local political and ethnic leaders.
"We sent an open letter to the Rivers state government on the 15th (of September), after our sources on the ground reported 500 dead in the last few weeks," Mr Ngwa said by phone from London.
Local officials have confirmed several incidents over the last month, but the combined death toll comes nowhere near the figure cited by Amnesty.
Many of the gangs were originally armed to fight turf battles on behalf of politicians during last year's elections, and they recruit their fighters from young disillusioned men in the impoverished delta.
Rivers state Governor Peter Odili earlier this month ordered top members of his government to leave office in what was described as a purge of public figures linked to criminal gangs.
Although the violence in the eastern delta has not halted exports, ethnic clashes in the western delta last year forced oil multinationals to temporarily shut in 40 per-cent of output.