Newsweek/The Niger Delta is once again under siege. Seven years on from the end of a sustained period of militancy—which saw oil workers kidnapped and production cut to less than a third of maximum capacity—a recently formed group is leading a fresh campaign of attacks in a bid to cripple Nigeria’s economy.

Smoke billows from a refinery in Port Harcourt, southern Nigeria, September 16, 2015. A new militant group calling itself the Niger Delta Avengers is wreaking havoc in Nigeria’s oil-producing region. PIUS UTOMI EKPEI/AFP/Getty Images

The upsurge in attacks by the group has coincided with a dramatic fall in oil production in Nigeria, traditionally the continent’s biggest producer. Petroleum Minister Emmanuel Ibe Kachikwu said earlier in May that production had fallen by 800,000 bpd to 1.4 million bpd, the lowest in two decades. It’s a drop that means Angola has at least temporarily taken over the mantle of Africa’s oil king.

The NDA follows the pattern of other groups, such as the Movement for the Emancipation for the Niger Delta (MEND), which led the militancy campaign in the mid-2000s. MEND and some of its most notorious leaders, such as Government Ekpemupolo—an ex-militant also known as Tompolo who is wanted on money laundering allegations totaling 46 billion naira ($231 million)—have disassociated themselves from the NDA. But according to Malte Liewerscheidt, senior Africa analyst at political risk consultancy Verisk Maplecroft, the group’s membership is likely made up of disaffected ex-militants who have not benefited from the presidential amnesty program that brought the previous campaign to a close in 2009. The amnesty included monthly subsidies to reformed militants, but also afforded lucrative security contracts to former leaders, like Tompolo, for protecting oil installations.

The NDA came to international attention after claiming an attack on an underwater pipeline run by Shell in February, forcing the Dutch oil giant to temporarily shut down its 250,000 bpd Forcados terminal. According to Liewerscheidt, the attack showed a level of sophistication and expertise that suggests the group may have insider knowledge of some of the international oil firms working in the Niger Delta. “[Forcados] was not just another pipeline somewhere out in the creeks, it’s right under the nose of the largest [international oil company] out there, namely Shell,” says Liewerscheidt. “[The NDA] have proven their capability to strike major targets again and again.”

As well as links with former Niger Delta militants, the group also appears to have connections with the pro-Biafra movement in southern Nigeria. The NDA has avowed its support for Nnamdi Kanu, the head of the Indigenous People of Biafra (IPOB), who has been in detention in Nigeria since October 2015 and is awaiting trial on charges of treason, which he denies. Pro-Biafra activists are campaigning for Kanu’s release and the realization of the independent state of Biafra, which was declared in southeast Nigeria in 1967 but was reintegrated into the country in 1970 following a devastating civil war.

“Operational links” exist between the NDA and IPOB, but the extent of these connections is not yet clear, according to Fulan Nasrullah, an independent conflict researcher based in Nigeria. “Publicly, the NDA has declared support for the Biafran struggle, while maintaining its separate agenda focusing on the Niger Delta,” says Nasrullah. If the NDA were to gain IPOB’s support, its manpower could be dramatically increased; thousands of people have taken part in protests in Nigeria demanding Kanu’s freedom, and IPOB has previously claimed to Newsweek that its global membership numbers in the millions, though this has not been independently confirmed.

Nigerian President Muhammadu Buhari has vowed to take harsh action against oil militants like the NDA. The president and leader of the All Progressive Congress party said in April that the “vandals and saboteurs” responsible for attacking oil pipelines would be dealt with “the way we dealt with Boko Haram.” Nigeria’s military has reclaimed much of the territory once held by Boko Haram under Buhari’s administration and has inflicted numerous casualties on the group, though Boko Haram continues to carry out occasional suicide bombings in the country’s volatile northeast.

While he has allowed the amnesty program to continue, Buhari has cut the subsidies and ended the handing out of security contracts to ex-militants. “[Buhari] has no interest in returning to the negotiating table,” says Liewerscheidt. “Both the actual costs of reinstating the amnesty program [to its former level], as well as the political costs, are now much too high for the government.”

Nigeria is heavily dependent on oil for its economy—petroleum products make up more than 90 percent of the value of the country’s total exports—and the recent fall in production has shown the ability of the NDA and others to impact upon the West African country’s most vital industry. Recent events suggest that the NDA is likely to pose an economic, as well as a security, threat to one of the world’s most important oil hubs.