JEM, or the Justice and Equality Movement, denied any involvement in the attack on the AU base in the eastern Darfur town of Haskanita when it happened in late September.

JEM leader Khalil Ibrahim repeated the denial on Monday, saying:"It was not JEM who attacked the base and we can prove it."

He blamed commanders behind a breakaway faction from his group. "They still call themselves JEM and used vehicles marked with JEM. They carried out the attack to make a name for themselves."

The attack was the worst single assault on AU peacekeepers in Darfur and came just weeks before planned peace talks between insurgent groups and Sudan's government.

At the time, diplomats said the most likely culprits were splinter groups of JEM and the Sudan Liberation Army's Unity (SLA-Unity) faction that may have attacked without the go-ahead of their central command.

The new details came in a monthly report on Darfur by U.N. Secretary General Ban Ki-moon that was distributed to journalists in Khartoum on Monday.

The report stated: "Preliminary results of an investigation initiated by the AMIS (African Union Mission in Sudan) Force ... suggest that the attack was conducted by rebels entering the camp in vehicles bearing the inscription "JEM".

"The motive of the attack appears to have been looting of AMIS logistical equipment."

The underequipped African force of around 7,000 troops from 26 countries patrolling Darfur, a region the size of France, is due to be replaced next year by a "hybrid" 26,000-strong AU-UN force.

The reort said the roll-out of the new hybrid force was now well under way. But it repeated concerns expressed by U.N. peacekeeping chief Jean-Marie Guehenno last week that the peacekeeping force was "at risk" unless disputes with Sudan over its make-up are resolved and key specialized units found.

International experts estimate 200,000 people have died in the Darfur conflict and 2.5 million driven from their homes, but Sudan says only 9,000 have died.