The agreement, Annan said, was reached in a gathering of African, Arab, European and UN leaders in Addis Ababa.
Annan had also said that the agreement could provide for a total of as many as 17,000 soldiers and 3,000 police officers.
Currently, the AU has just 7,000 troops in the region.
Sudan had previously refused to allow non-African troops to enter Darfur, saying they would be "neocolonialists".
The existing AU troop strength in Darfur is considered to be inadequate and ineffectual.
"The Sudanese government has not agreed to the deployment of international troops"
Sudan Deputy Foreign Minister
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Major-General LFK Aprezi, the AU commanding officer, said he urgently needed more troops as the security situation on the ground, particularly in western Darfur, continued to deteriorate.
In recent days, pro-government militias known as Janjawid have stepped up attacks on villages in Darfur, killing dozens of people, international observers said.
The Sudanese army has denied any connection to Janjawid attacks, saying the claims were politically motivated.
An agreement to hold renewed talks among all parties to Darfur's conflict brings a historic opportunity to end fighting which has killed 200,000, the UN humanitarian chief said on Saturday.
A meeting in the Ethiopian capital Addis Ababa on Thursday agreed that a May peace signed by only one of three rebel factions was inadequate and a new process should be activated under joint leadership of the UN and African Union (AU).
"The DPA [Darfur Peace Agreement] is not sufficiently inclusive ... [and] this has led to insecurity, worsened the humanitarian situation and limited humanitarian access," the final communique of the meeting said.
The crisis in Darfur could become "infinitely worse" if the deal reached to send a mixed UN and African force to the war-torn region is not applied quickly, the UN chief of humanitarian affairs said on Saturday.
"This is the moment of truth for Darfur," Jan Egeland, UN undersecretary-general for humanitarian affairs, said in the Sudanese capital. "We are playing with a powder keg, it could get infinitely worse."
More than 200,000 people have been killed and 2.5 million displaced by three years of fighting in the vast, arid Darfur region of western Sudan. An ill-equipped African Union mission has achieved little in preventing the violence from worsening.