Nigeria's government and oil giant Shell Friday came under heavy pressure following the release of a landmark UN report detailing oil pollution that may require the world's biggest ever clean-up.
The report set out scientific evidence for the first time of devastating pollution in Ogoniland, part of the country's main oil-producing Niger Delta region where Shell and the state petroleum company have operated.
"UNEP believes that oil contamination in Ogoniland has created an environmental crisis of unprecedented proportions," Joseph Alcamo, UN Environment Programme chief scientist, told journalists in London.
"The problem is quite clear and now the question is what's the way out."
Anglo-Dutch Shell was forced to pull out of Ogoniland amid unrest in 1993, though pipelines for its Nigerian joint venture, which includes the state oil company, and other facilities remain there.
The UNEP report, which details urgent health risks such as badly contaminated drinking water, led some to raise the possibility of lawsuits that could now be brought against Shell or others with scientific evidence to back them.
"This is a wonderful intervention on the part of the United Nations, and this has also in a way confirmed the cries of the Ogoni people over the years," said prominent Nigerian rights lawyer Femi Falana.
"There is now a scientific basis backed by the UN.... I think this now provides an opportunity for people to make legitimate demands."
Shell faced criticism from UNEP, which said "control and maintenance of oil field infrastructure in Ogoniland has been and remains inadequate: the Shell Petroleum Development Company's own procedures have not been applied, creating public health and safety issues."
UNEP also called for the oil industry and the Nigerian government to contribute $1 billion to a clean-up fund for the region, adding that restoration could take up to 30 years.
"The environmental restoration of Ogoniland could prove to be the world's most wide-ranging and long term oil clean-up exercise ever undertaken", it said.
Shell maintained its stance that most environmental damage has been caused by oil theft, sabotage and illegal refining.
The managing director for its Nigerian joint venture, Mutiu Sunmonu, says in a Shell video posted on YouTube that until illegal activity is brought under control, "there is little that can be done to bring an end to the problem of spills."
A UNEP spokesman told journalists Friday that the agency could not support Shell's assertion.
"UNEP would challenge that," said Nick Nuttall. "We don't have the data to say where the oil came from in any kind of comprehensive way, either historically or currently.
"... The fact is that the assertion of SPDC yesterday that it's largely or mainly from illegal activities, well, we can't support that statement."
SPDC is Shell's Nigerian joint venture, the Shell Petroleum Development Company.
The study of the effects of pollution in Ogoniland follows a two-year assessment by UNEP in the region of mainly farmers and fishermen.
The Movement for the Survival of the Ogoni People, which has long pushed for action in the region, said it was not nearly enough.
It said in a statement that "what is needed and the Ogoni expectation is the cleanup of our devastated environment and not a mere study to tell us what we know."
The group also called for Shell's license in Nigeria to be revoked.
Ogoniland was the native region of Ken Saro-Wiwa, the renowned environmental activist who was executed by a Nigerian military government in 1995 after what was widely considered a show trial, drawing global condemnation.
His activism and execution drew the world's attention to Ogoniland.
His son, Ken Saro-Wiwa Jr, now works as an adviser to President Goodluck Jonathan, the first head of state from the Niger Delta.
He called the report a "vindication" and expressed confidence the government would take action.
"I think he is looking down on the whole thing and smiling widely to himself," Saro-Wiwa Jr told AFP, speaking of his father.