The Niger Delta Avengers announced that they blew up two Chevron oil wells.

The militant group took credit for the attack in a series of tweets on Wednesday.

Reuters reports that an oil spill was seen in waterways and wetlands near the Chevron sites following the reported attack.

The exact volume spilled is so far unclear.

Some Niger Delta residents have been pushing for foreign energy companies to leave the region. And this attack comes a few days after the NDA’s deadline for all foreign oil companies to vacate the Niger Delta.

The NDA previously targeted a Chevron offshore facility in mid-May and the underwater Forcados export pipeline operated by Shell in late March.

Nigerian oil production has fallen by 46% this year to about 1.1 million barrels a day (as of Monday), down from 2.03 million barrels a day in January. That’s such a huge drop that Angola is now the No. 1 producer in Africa, as its production held steady in April at 1.8 million barrels a day.

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