Amnesty International has accused Royal Dutch Shell’s of making false claims concerning its spills clean-up in Nigeria, even citing a contractor who says the clean-up itself was a cover-up, reported ABC News.

In a new report, Amnesty says that the Ogoniland area is still blighted despite Shell’s claims that it decontaminated the location 40 years ago, and a second time after a 2011 UN investigation found massive pollution.

Amnesty adds that Shell Nigeria does not use the same standards as its European parent company.

According to Bloomberg the four clean-up sites in question are all in the crude-producing Niger River delta.

Amnesty timed the release of its Tuesday report to coincide with the 20-year anniversary of the death of Ogoniland activist and environmentalist Ken Saro-Wiwa.

Saro-Wiwa had campaigned for oil-spill compensation and was hanged by the then military government.

In marked contrast, the Nigerian President Muhammadu Buhari said in August that he’s accelerating plans to rid the area of pollution in one of the world’s largest clean-up operations.

Precious Okolobo, a Lagos-based spokesman for Shell, explained that Shell “is committed to cleaning up all spills from its facilities, irrespective of cause,” adding that this is “equally the case in Ogoniland, despite the fact that we ceased producing oil and gas there in 1993.”

Idris Musa, director of oil-field assessment at Nigeria’s National Oil Spill Detection and Response Agency (NOSDRA), declined to comment.

ABC News also quoted Amnesty’s charge that the Nigerian government, the majority owner in Shell Nigeria, was guilty of an “almost complete failure” to regulate the industry and protect people’s rights.