LONDON, May 15 (Reuters) - Angola became Africa's largest oil producer last month, OPEC said on Thursday, as unrest sharply cut Nigerian output.

Angola, one of OPEC's newest members, claimed the top spot for the first time pumping 1.873 million barrels per day in April, 55,000 bpd more than Nigeria.

While Angola has gradually increased its production with new offshore oilfields, Nigeria has been plagued by persistent supply disruptions.

Production in Nigeria, Africa's top producer since 1978 on an annual basis, tumbled by as much as 1.36 million bpd in late April or more than 40 percent of its installed output capacity.

Militant groups have been on a violent campaign in the oil-producing Niger Delta since 2006 to press for greater local control over oil revenues and development for the impoverished region, where they say five decades of oil extraction have polluted the land and water, and enriched corrupt politicians.

Most analysts believe Nigeria will retake the top position this month as much of its shut-in production has been restored.

Some 800,000 bpd has since come back online after Exxon Mobil (XOM.N: Quote, Profile, Research) and its union workers reached an agreement to end an eight-day strike.

Royal Dutch Shell (RDSa.L: Quote, Profile, Research) also said on Tuesday it has brought back some of its shut-in production, repairing two of four Bonny Light oil facilities damaged by militant attacks. (Reporting by Randy Fabi; editing by James Jukwey)

Angola surpasses Nigeria as top Africa oil producer | Industries | Energy | Reuters