Witnesses say an explosion has closed a second Chevron facility in Nigeria as renewed attacks by militants further cut production in Africa's biggest petroleum producer.

Production already had reached a 20-year low because of attacks on a Chevron platform last week and on a pipeline that forced Shell to suspend exports of Bonny Light on Wednesday. Shell's Forcados export terminal has been shut since a February bombing.

Villagers said militants attacked a Chevron well on Marakaba pipeline Thursday. They requested anonymity for fear of repercussions.

Meanwhile, Exxon Mobil on Friday said some production of Qua Iboe crude has halted because a drilling rig damaged a pipeline. The company declared force majeure, protecting it from contractual obligations.