Niger Delta Avengers Militant group says it blew up 2 Chevron wells The attacks have reduced Nigeria's total oil output to below that of rival producer Angola, sharply affecting the national budget which relies on oil tax revenue.

A Nigerian militant group said on Wednesday that it had blown up two Chevron oil wells in the second such attack in a week on the company's facilities in Nigeria's oil-producing Delta region.

An oil spill was seen in waterways and wetlands surrounding the Chevron sites after the attack, according to a Reuters witness and a local official, though the volume spilled could not be immediately determined.

The attacks occurred as tensions flared between international oil companies and Niger Delta residents, some of whom are pushing foreign energy companies to leave Africa's largest economy in a bid for greater economic self-reliance.

A group calling itself the Niger Delta Avengers said in a post on Twitter that it used "100 Gunboats, 4 Warships and Jet Bombers" to attack Chevron's RMP 23 and 24 wells early on Wednesday morning. It claimed the wells were Chevron's highest-producing in the country.

The attacks have reduced Nigeria's total oil output to below that of rival producer Angola, sharply affecting the national budget which relies on oil tax revenue.

The Niger Delta Avengers, a relatively new radical group that has claimed responsibility for a number of pipeline bombings in the country this year, had told Chevron and other oil companies to leave Nigeria by the end of May.

Last week the group claimed responsibility for blowing up electricity feeds to Chevron's facilities, forcing the company to shutter onshore operations.

Attacks carried out by the group since February have cut Nigeria's oil output by at least 300,000 barrels of oil per day (bpd) and shuttered two refineries. The group has also attacked facilities owned by Royal Dutch Shell.

The wells attacked on Wednesday are in the Dibi field near Warri, about 265 miles (426 kilometers) southeast of Lagos, Nigeria's largest city.

Local residents confirmed to Reuters that an attack had taken place.

In response to a request for comment, Chevron spokesman Kurt Glaubitz said, "As a matter of long-standing policy, we do not comment on the safety and security of our personnel and operations."

It was not clear what effect the attacks would have on Chevron's daily Nigerian output. Last year Chevron pumped about 224,000 bpd in Nigeria, about 9 percent of the company's global output.

Militancy has been rife over the past decade in the Delta, one of the country's poorest areas despite generating 70 percent of state income.