The United Nations' (UN's) human rights office on Tuesday accused forces allied with Sudan's government of mass abduction and rape of women and girls in Darfur, acts it said could constitute war crimes.

Its latest report, based on testimony from victims and witnesses, called on Khartoum to investigate reports that about 50 women were forced into "sexual slavery" after an attack on the rebel-held town of Deribat in South Darfur's Jebel Marra region last December.

The abductees, who included many children, were held for about one month, and beaten and raped repeatedly, often in front of each other, the report from the office of UN High Commissioner for human rights Louise Arbour said.

"Witnesses indicated that the abduction, rape and other human rights violations that continued throughout the period were committed by the same group of men who conducted the actual attack," it said.

The report concluded that the Sudanese government bore responsibility for the abuses committed by the official Popular Defense Forces (PDF) militia and the Abu Gasim faction. Sudan's army had provided air and ground support for the raids which resulted in 36 civilian deaths.

The UN report named three men as possibly sharing criminal responsibility for leading the attacks on Deribat, and the abductions and sexual abuse.

"A series of violations have been committed that constitute both violations of international human rights law and international humanitarian law. Some of these may also constitute war crimes", it said.

"The government should issue immediate clear instructions to all troops under its command including PDF and other militias that rape and other forms of sexual violence will not be tolerated, that they constitute war crimes," it continued.

An estimated 200 000 people have died and 2,5-million have fled their homes in Darfur since mostly nonArab rebels took up arms against the government in the vast western region in 2003.

Sudan denies mass rapes in Darfur. On Monday Justice Minister Mohamed Ali al-Mardi said that reports by international rights groups on abuses were "criminal."

"All reports...about genocide and mass rape are frivolous and obviated by malice," he told Reuters. "They are executing policies of other nations like the US ... against Sudan."

The UN report said a "pattern of mass abduction" which began with the Darfur conflict, appeared to be ongoing. The report covers a six-month period ending in May 2007.

The victims in Deribat, who were mainly from the Fur tribe, may have been targeted because the Fur community in Jebel Marra has been perceived as sympathetic to Sudan Liberation Army rebels who stayed outside the 2006 Darfur peace deal, it said.

Jebel Marra region is a stronghold of Abdul Wahed Mohammed el-Nur, leader of a faction of one of the Darfur rebel groups. The top US envoy for Darfur Andrew Natsios, last month accused Sudan of bombing civilian targets in the area.

The UN report also called for the African Union to deploy troops in the area, but noted they currently had "no presence in Jebel Marra as they consider it unsafe, leaving the civilian population unprotected and at the mercy of attackers".