US oil giant Chevron has halted onshore oil production at its Escravos oilfield after an attack on a pipeline. The loss could equate to about 120,000 barrels per day, about 6.6% of Nigeria's total daily crude production. The Nigerian military said militants blew up the Niger Delta pipeline, but the region's main armed group blamed angry youths for the attack. Earlier this week, Nigeria's president ordered tighter security in the Delta after an attack at a Shell facility. According to the BBC's Alex Last, in Lagos, sources in the western Niger Delta believe the latest attack is the work of illegal oil "bunkerers" - involved in the lucrative trade in stolen oil.