Caroline Hawley reports on a sensitive subject for the Khartoum government

Leonardo Franco, the UN's investigator into human rights in Sudan, said the country's government bore the "largest share of responsibility" for the slave trade, partly caused by the 16-year-old civil war in the south.

Addressing the UN Human Rights Commission in Geneva, Mr Franco said civilian targets, including hospitals, had been bombed, child soldiers conscripted and women and children abducted into slavery. He called on the Khartoum government to stamp out the slave trade.

Slaves change hands for around $50

The Sudanese Government has consistently denied the allegations.

Last month a government committee called on the UN children's agency, Unicef, to retract a statement alleging it had irrefutable evidence of a continuing slave trade.

Mr Franco said that slavery had, historically, been a feature of tribal rivalry in Sudan - but the war had revived and exacerbated the practice.

"There is ample and consistent evidence that the war is conducted in total disregard to human rights and humanitarian law principles," said Mr Franco.

"Violations are perpetrated by all parties involved in the conflict, the government and groups under its control bearing the largest share of responsibility."

'Predatory attacks'

The Argentinian rapporteur praised the Sudanese Government for their co-operation during his visit to the southern garrison town of Wau in February.

But he told the 53-nation human rights commission that the government had been using nomadic tribesmen known as muraheleen from the north of the country to escort a military train supplying Wau in the province of Bahr el-Ghazal - mainly inhabited by Dinka farmers and cattle herders.

"As war booty in exchange for their services, the muraheleen are given free rein to perpetrate destructive and predatory attacks against the civilian population," he said.

"This includes the abduction of women and children who are taken up north to be subjected to forced labour or other conditions amounting to slavery."

Investigation