The U.N. human rights chief is calling on Sudan's government to investigate possible atrocities committed in the war-torn Darfur region.

A statement Friday by Louise Arbour says a team of U.N. investigators documented at least 15 cases of rape in the western Jebel Marra area last December. The alleged victims were as young as 13, and included at least two pregnant women. The victims described their attackers as soldiers wearing military uniforms.

Arbour is also demanding information on 19 men allegedly seized last September by the Sudan Liberation Army - a rebel group which signed a peace deal with the Somali government last year.

Eight of the men taken in the southern Darfur town of Geraida were said to have been found dead. Arbour says there have been reports some detainees were tortured.

Arbour says Khartoum should conduct "an impartial, timely, and transparent" investigation into the alleged rapes, which she describes as a "weapon of war" intended to humiliate the local population.

She is also calling on SLA leader Minni Minnawi to allow the U.N. access to any detainees to ensure their well-being. If the men are dead, Arbour wants Minnawi to find out who was responsible and bring them to justice.

Darfur has been torn by four years of fighting between government-backed militias and rebel forces that have left more than 200,000 people dead and displaced more than two million others. A recent U.N. report accused the Sudanese government of orchestrating attacks on civilians in Darfur. Khartoum denies the allegations.

Some information for this report was provided by AFP and AP.