Nigeria’s militant group Niger Delta Avengers (NDA) claimed via Twitter that it had blown up two oil wells operated by US company Chevron located in the Dibi field near Warri, a city in Delta state, southern Nigeria, NewsWeek reported.

An oil spill was seen in the area surrounding the Chevron sites following the attack, Reuters reported, though Chevron have not confirmed the attack. The NDA have threatened Chevron and other international oil companies with “bloody” attacks if they do not pull out of the Niger Delta and the group claimed an attack on another Chevron facility on May 25 that reportedly resulted in the company’s onshore operations being “grounded.” The group has also attacked facilities run by oil giant Shell in the restive region.

Production at the OPEC-member had already fallen from a projected 2.2 million barrels a day (MMBPD), to 1.4 MMBPD before the latest attacks on the oil industry in southern Nigeria, including three within the past week on facilities belonging to Chevron, Kallanish Energy wrote.

The information came the same day Nigerian President, Muhammadu Buhari, has cancelled at the last minute a visit planned to the oil-producing Niger Delta, which has been hit by a wave of militant attacks. A Presidential source told SaharaReporters that President Buhari will be represented by the Vice President, Prof. Yemi Osinbajo.