Mr Saro-Wiwa had led a successful campaign against Shell's activities in his homeland, even forcing the company to quit Ogoniland in 1993.

ECONOMIST: A payout could encourage others

In response to Thursday's report, Mr Sunmonu said it made a "contribution towards improving understanding of the issue of oil spills in Ogoniland".

BBC: Nigeria Ogoniland oil clean-up 'could take 30 years'

The campaign forced Shell to stop pumping oil out of Ogoniland but it continues to operate pipelines in the region and spills have continued.

BBC: Nigeria Ogoniland oil clean-up 'could take 30 years'

But earlier, Unep spokesman Nick Nuttal told the BBC's Network Africa that the study was not intended to "blame any particular stakeholder operating in Ogoniland".

BBC: Nigeria Ogoniland oil clean-up 'could take 30 years'

There has been a mixed reaction to the settlement in Ogoniland.

ECONOMIST: A payout could encourage others

One reason for the perception that the NDDC has done nothing for Ogoniland could be that, although many projects were ready a year ago, they only started being commissioned in March.

BBC: Nigeria's elections in the south

It was the only company operating in Ogoniland, and no oil has been pumped there since, yet the locals continue to complain of oil spilling from the maze of pipes criss-crossing their land.

CNN: Nigerians angry at oil pollution double standards

Last year, a report by the United Nations Environment Programme said that over half a century of oil operation in the region, by firms including Shell, had caused deeper damage to the Ogoniland area of the Niger Delta than earlier estimated.

BBC: Nigeria oil spills: Shell rejects liability claim