The Nigerian army has arrested several suspected members of a militant group called the "Niger Delta Avengers" (NDA), thought to be behind recent attacks on oil pipelines in the south. The country's oil production has been severely disrupted by the attacks. US oil giant Chevron shut down an offshore platform this month after an attack claimed by the Avengers group. Many militants joined an amnesty programme in 2009 after an insurgency in the oil-rich delta region.
Nigeria has long been Africa's largest oil producer, but its economy is currently facing difficulties due to the recent drop in global oil prices. Most of Nigeria's oil wealth comes from the Niger Delta, an area which remains poor and underdeveloped. Previous insurgent groups said they were fighting so local people could benefit more from their region's natural resources.
Oil spills have also resulted in environmental devastation over the years. The amnesty programme, which provides tens of thousands of former oil militants with a monthly stipend from the government, stemmed the level of violence in the region after its introduction in 2009. But in the latest budget, Nigerian President Muhammadu Buhari reduced funding for the programme by 70%, and has spoken of phasing it out entirely by 2018.
Critics accuse Mr Buhari, a Muslim northerner, of unfairly targeting communities in the southern, mainly Christian oil-producing regions, as part of his anti-corruption drive. Mr Buhari's predecessor Goodluck Jonathan, a Christian, comes from the Niger Delta region. Little is known about the so-called "Avengers", who say they are fighting for an independent Delta region. But the attacks claimed by the group have contributed to a slump in Nigerian oil production, reportedly down to its lowest level in more than two decades.