Amnesty International on Tuesday called for Shell to be prosecuted for allegedly helping Nigeria's military to commit human rights abuses in the oil-rich south in the 1990s.

The London-based global rights watchdog said the oil giant should be tried in Nigeria, as well as Britain and Netherlands where it has its head office. 

Shell's Nigerian subsidiary strongly denied the charges, calling them "false and without merit".

Audrey Gaughran, director of global issues and research at Amnesty, said it was "indisputable that Shell played a key role" in events in Ogoniland in the 1990s.

"But we now believe that there are grounds for a criminal investigation," she added in a statement after publishing a cache of documents relating to the turbulent period.