A human rights group has sued three US companies in federal court in Los Angeles to force them to step up efforts to end child labour on African farms that supply cocoa beans used to make chocolate products, the Reuters news agency reported.

The International Labor Rights Fund filed suit on behalf of former child labourers against Nestle, Archer Daniels Midland and Cargill. on Thursday claiming the companies are involved in trafficking, torture and forced labour of Mali children who were enslaved to work on Ivory Coast farms.

The lawsuit comes soon after the US and European chocolate and cocoa industry missed a 1 July deadline imposed by federal law for adopting protocols to eliminate child labour from the West African cocoa supply chain.

US senator Tom Harkin, one of the protocol's authors, said earlier this month he was disappointed that the industry had been unable to certify that its chocolate products were not made with child labour but was satisfied it was "committed to moving forward."

In a statement, the International Labor Rights Fund blasted the industry for dragging its feet and refusing "to exchange a small portion of its massive profits to ensure sufficient return for farmers and workers."

Representatives for Archer Daniels Midland of Decatur, Illinois, one of world's largest agricultural processing companies, and Cargill, an agricultural products and services provider, had no comment on the lawsuit.

A Nestle spokeswoman also would not comment on the lawsuit, but said the company was working with the International Cocoa Initiative foundation created by the Harkin-Engel protocol.

"Obviously we strongly believe it is important to make sure that cocoa is grown responsibly without abusive labour practices," Nestle spokeswoman Barb Skoog said.

The lawsuit claims the Mali children were beaten and forced to work 12 to 14 hours a day with no pay and little food or sleep.

The three main plaintiffs said they were ages 12 to 14 when were taken from their homes, but the lawsuit covers "thousands" of children who were allegedly enslaved from 1996 until the present to work in the Ivory Coast region.