"We condemn this senseless and premeditated savage attack", which destroyed everything in the rebel-held village of Khor Abeche but the mosque and the school, the organisations said in a joint statement on Friday, vowing to refer the militia commander to the UN Security Council for possible sanctions.
The statement for the first time in the troubled region named the commander, identifying him as Nasir al-Tijani Abd al-Qadir of the Misairiya tribe, based in the militia stronghold of Nitega.
The Security Council recently has voted to impose a travel ban and an asset freeze on those responsible for atrocities against civilians or cease-fire violations in Darfur and to refer those responsible for war crimes to the International Criminal Court in The Hague.
Thursday's raid came days before wealthy nations were to gather in Oslo to pledge aid to rebuild southern Sudan, devastated by a separate conflict that ended early this year.
The Darfur attack appeared to be in retaliation for the alleged theft of 150 head of cattle, which the fighters blamed on Khor Abeche villagers, the AU-UN statement said.
Al-Tijani also accused Sudan Liberation Army rebels of refusing to return the bodies of two of his men, killed in March in an earlier attack on Khor Abeche, it said.
The African Union had planned to deploy peacekeepers to Khor Abeche and Nitega before the attack but was prevented from doing so "by what can only be inferred as deliberate official procrastination over the allocation of land for the troops' accommodation," according to the statement.
African Union Ambassador Baba Gana Kingibe and UN envoy Jan Pronk said Sudan's government should take action against al-Tijani, accusing him of repeatedly threatening the village's destruction before actually doing so on Thursday.
More than 180,000 people have died in Darfur from hunger and disease over the past year and a half, and more than 2 million have fled their homes to makeshift camps in the remote, western desert region, according to UN estimates.
More than 180,000 people have
died in Darfur since early 2003
The crisis was triggered in February 2003, when pastoral rebel groups took up arms against the government in a struggle over power and scarce resources.
Khartoum retaliated by arming nomadic militia that are accused of a campaign of murder, rape and arson against villagers that the United States has called genocide.