By Tife Owolabi
YENAGOA, Nigeria (Reuters) - An explosion rocked a Chevron oil pipeline in Nigeria's restive Delta region on Friday, a security source said, the second blast at a facility of the U.S. oil major within a week, feeding concern over a revived militant campaign in the area.
The swamps of the southern Delta have been hit by a series of militant attacks on pipelines and other oil and gas facilities that have reduced Nigeria's output by 300,000 barrels a day and closed a major export port and two refineries.
Last week, militants calling themselves the Niger Delta Avengers claimed an attack on a Chevron Platform in the Delta.
The group has warned oil firms to leave the region within two weeks and says it is fighting for independence for Delta. It had earlier said it wanted a greater share of oil revenues and an end to oil pollution.
The attacks have driven Nigerian oil output to near a 22-year low and, if the violence escalates into another insurgency, it could cripple output in a country facing a growing economic crisis.
On Friday, a new blast occurred at a Chevron oil well at the Marakaba pipeline in Warri, a security source told Reuters. No more details were immediately known.
Chevron had no immediate comment, while Nigeria's army, which has stepped up its presence in the region, could not immediately be reached for comment.
A day before, the "Avengers" had warned Chevron on their website against repairing the last week's damage.
"We made it clear that no repair works should be done until our demands are fully met," the group said in a statement. "We are ready to destroy more pipelines, we won't only destroy pipelines, but will bring the fight to your tank farm and your (local) headquarters in Lekki, Lagos."
The group has staged sophisticated attacks that have closed Shell's 250,000 bpd Forcados terminal and two local refineries. Shell and Chevron have both evacuated staff, according to labour unions.
Little is known about the radical group, and efforts by Reuters to reach it have been unsuccessful.
Crude sales from the Delta account for around 70 percent of national income in Africa's biggest economy but residents, some of whom sympathise with the militants, have long complained of poverty and neglect.
President Muhammadu Buhari has extended a multi-million dollar amnesty signed with militants in 2009 but upset them by ending generous pipeline protection contracts.
(Reporting by Tife Owolabi; additional reporting by Terri Wade; Writing by Ulf Laessing; Editing by Mark Heinrich and Hugh Lawson)