"There is a protection crisis in Darfur today, in terms of us not being able to adequately protect the displaced civilian population," the official, Dennis McNamara, told a press conference in Nairobi.

"There remains constant regular pressure, sometimes harassment by the authorities in various locations in Darfur, on displaced populations to go back to insecure villages of origin," he explained after a visit to the region.

McNamara, the special advisor on displacement to UN Emergency Relief Coordinator Jan Egeland, said displaced people were "traumatised" in Darfur, where rebels have been fighting and government troops, backed by militia called Janjaweed, for the past 18 months.

McNamara said "sexual violence and rape against women and girls" were common, adding: "We have an example of a girl as young as seven credibly reported as a rape victim. Most rapes are multiple rapes and done by many men, usually militia," he added.

"Attacks, including particulary sexual violence and rape, are undertaken with impunity," he said, explaining that no exact figures are available.

Meanwhile, a 155-strong company of Nigerian infantry flew out of Abuja yesterday, heading for the war-torn western Sudanese region of Darfur to join an African Union force protecting ceasefire monitors.

"You are going to Sudan purely to assist our brothers and sisters in restoring a hope that is fast diminishing in them," Brigadier General Shekari Biliyok, commander of the Army Headquarters Garrison, told his troops.