Burkina Faso's President, Blaise Compaore, head of the AU's security committee, said after a mini-summit on the fringes of the UN General Assembly that the force would receive logistic and material support from the United Nations.
President Compaore also said the AU obtained a commitment from Arab states to finance the operation. Arab nations have promised funding in the past.
But so far only NATO countries have helped with transport and other aid.
The mandate for the AU force of some 7,000 troops expires on September 30.
Bashir again rejects UN force
Sudan's President Omar Hassan al-Bashir, who has rejected a UN force in Darfur, attended part of the meeting and again said he would not allow UN troops into Darfur.
But Mr Compaore said Sudan is "disposed" to work with the United Nations, without elaborating.
"All of the negotiations and all of the contacts we have had clearly indicated that they are willing and are disposed to work together with the United Nations," he said.
More than 200,000 people have died in Darfur from the conflict or disease and 2.5 million have been forced from their homes into squalid camps in a campaign the United Nations calls the worst human crisis and the Bush administration labels as genocide.
The UN Security Council last month authorised a force of up to 22,500 soldiers and police officers under United Nations command to take over Darfur operations from the AU troops.
But Sudan's consent was set as a condition for a UN takeover and
UN officials have said no troop contributors would go to the region without Khartoum's permission.
At a news conference at the United Nations, President Bashir said the Khartoum government would approve an extension of the AU force but adamantly rejected an eventual transition to a UN force, saying it was a cover for aiding Israel.