Amnesty International has said oil giant Shell must not be allowed to “palm off its responsibility” for past spills in the Niger Delta region of Nigeria.
It comes ahead of a response set to be outline by the Nigerian Government following a United Nations Environment Programme (UNEP) report.
The West African country is due to start a clean-up of the Ogoniland tomorrow.
Shell has declined to comment on the allegations made by Amnesty International.
Last month, President Muhammadu Buhari said a clean-up programme would begin this month.
It was originally called for in 2011 by UNEP after it published a report which showed there had been high levels of pollution caused by oil spills from Shell pipelines in the Ogoniland region.
Amnesty International business and human rights campaigner Joe Westby said: “The Niger Delta is one of the most oil-polluted places in the world.
“That is because companies like Shell are failing to prevent or clean up spills years, sometimes decades, after they happen. Shell cannot rely on the Nigerian government to clean up its dirty work for it.
“The tragedy is that the oil spills continue to destroy the livelihoods of thousands of local people to this day.
“Shell will tell you that the vast majority are a result of theft, even though Amnesty International has repeatedly published evidence showing Shell misstates the cause of oil spills.
“But whatever their cause, Nigerian law still says that the company who operates the pipeline has to clean up. That is something Shell has failed to do for decades.
“The start of the clean-up is a much-needed, long-awaited step for people who have lived with polluted waters and farmlands for decades.
“They have a right to be sceptical, they have seen clean-ups promised and people paid to do the work in the past, only for little improvements to be delivered.
“This time the rhetoric must translate into action on the ground.”
Earlier, the boss of Shell’s Nigerian operations said production had been hit by a recent spate of attacks by a terrorist group called the Niger Delta Avengers.