String of attacks by group – who claim to fight for environment and local people – have pushed down Nigeria’s oil output

Members of the Nigerian militant group the Niger Delta Avengers have shut down facilities owned by one of the world’s biggest oil companies.

People living near Chevron’s Escravos terminal in the oil-rich southern Nigerian region of the Niger delta reported hearing a loud blast during the night. Chevron confirmed on Thursday morning that the attack, which was on its main electricity power line, had shut down all its onshore activities.

“It is a crude line which means all activities in Chevron are grounded,” a company source told Reuters.

It was the latest in a string of attacks by the Avengers, who have demanded that foreign oil companies leave the Niger delta before the end of the month, and say they are fighting to protect the environment and to win locals a bigger share of the profits.

The group has helped push the country’s oil output to its lowest level in decades. According to Emmanuel Ibe Kachikwu, head of the state-run oil company, the attacks have reduced the number of barrels produced a day from 2.2m to 1.4m. As well as hitting Nigeria’s economy – which, analysts have warned, is headed for a full-blown crisis – the attacks on Africa’s biggest petroleum producer have led to a rise in global oil prices.

The latest attack comes as Nigeria’s president, Muhammadu Buhari, prepares to celebrate a year in office this Sunday. He won the 2015 election on a promise to fight corruption and the bloody conflict waged by the Islamic militant group Boko Haram in the country’s north-east, and took over when Nigeria was in the midst of an economic crisis largely caused by the then falling price of oil, which the government relies on for 70% of its revenue.

Although he said Boko Haram had been “technically defeated” and claimed the recent escape of one of the kidnapped Chibok girls as a victory for his government, Buhari has been struggling to revive the flailing economy.

Under an amnesty deal reached in 2009 with other militants who were attacking oil facilities, the government paid millions of dollars to the leaders to “guard” oil companies’ infrastructure – in effect paying them not to attack it. Buhari has extended the deal, but cut its budget, giving rise to a potential source of anger in the region.

It is not known who finances the Niger Delta Avengers, but it has issued threats via its website and social media.

“Be informed that if we decide to strike it [is] going to be bloody ... If you continue to undermine us and go ahead with the repair works you won’t see us coming but we are coming for you,” the group’s spokesman, Murdoch Agbinibo, said in a statement entitled “Chevron, don’t dare the Avengers” two weeks ago.

In a follow-up tweet, the group said on Thursday: “We warned Chevron but they didn’t listen. The Niger Delta Avengers just blew up the Escravos tank farm main electricity feed pipeline.”

On its Twitter account, Nigeria’s main opposition party, the People’s Democratic party, which was in power for 16 years prior to the 2015 election, accused Kachikwu of giving representatives of the Avengers a $10m bribe and appealing to them to stop the attacks. These allegations have not been substantiated.