UNITED NATIONS - Ugandan rebels notorious for mutilating their victims and abducting children have found a safe haven in Sudan's western Darfur region, an anti-genocide group said in a report that Khartoum dismissed as a lie.

A contingent of the feared Lord's Resistance Army "has taken refuge in areas of south Darfur, Sudan, controlled by the government of Sudan," the Washington-based Enough Project said in the report, an advance copy of which was provided to Reuters on Wednesday.

"The possibility of rekindled collaboration between LRA leader Joseph Kony and Sudanese President Omar (Hassan) al-Bashir ... should alarm policymakers and demands urgent international investigation and response," it said.

Both Bashir and Kony are wanted for war crimes and crimes against humanity by the International Criminal Court in The Hague.

"The Khartoum regime's principal tool of war during its 21-year reign has been support for marauding militias such as the Janjaweed, the Murahaleen, and the Lord's Resistance Army," said John Prendergast a former U.S. State Department official who co-founded the Enough Project.