Nigeria's environment minister Amina Muhammed has visited the Ogoniland region in the oil-rich Niger Delta, which has has been badly affected over the years by oil spills. .

Oil giant Shell has been sued by residents who are demanding hundreds of millions of dollars in compensation. It denies full responsibility for the spills.

A UN report in 2011 said the Ogoni communities faced a severe health risk, with some families drinking water with high levels of carcinogens.