An extra 4,000 troops will be added to the Darfur mission, bringing the number of police and soldiers to 11,000.
On Monday, Assan Ba, spokesman for the African Union (AU) in Addis Ababa, said: "The Peace and Security Council of the AU ... has endorsed the new concept of operation, extending the duration of stay of the African Mission in Sudan up to December 31, 2006, and to boost the troop level by six battalions."
One battalion consists of 680 troops.
The AU said the soldiers would come from countries already contributing troops in Darfur - Nigeria, Rwanda, South Africa and Senegal.
An estimated 200,000 people have died in Darfur since violence flared in 2003.
About 2.5 million people have been displaced in the fighting between government forces, rebels and militias.
The AU expansion follows pressure on Sudan to allow a force of 20,000 UN troops into Darfur to replace 7,000 AU troops in the region who have monitored a fragile ceasefire.
"Any American official who comes to Sudan, we will stamp his passport for only 25km from the presidential palace"
Omar Hassan al-Bashir,
The Sudanese government has stood firm on its refusal to allow UN forces into Darfur, calling it a Western ploy to re-colonise Sudan.
The AU's mandate in Darfur had been set to expire on September 30, and the pan-African body had said it could not continue beyond October because it was out of money and needed more equipment such as helicopters.
With aid experts predicting a new humanitarian catastrophe in Darfur if African troops withdrew, the AU agreed last week to extend its mission until December 31, with logistical and material support from the UN and funding from Arab states.
Nassir Abdulaziz al-Nasser, Qatar's UN ambassador, said around $50 million had been raised for the force among Arab nations that aimed at raising $100 million.
Efforts were to continue on Monday at the UN to gear up for a possible mission transfer to a better-resourced UN force, with more than 140 countries expected to attend a meeting at the UN department of peacekeeping operations in New York.
"Time is running out. The violence in Darfur is not subsiding, it is getting worse," said Condoleezza Rice, US secretary of state on Friday.
"US time is running out. The violence in Darfur is not subsiding, it is getting worse"
Secretary of State
For his part, Omar Hassan al-Bashir, the Sudanese president, sounded a defiant note on Sunday night in the face of the international pressure, saying he would impose a travel ban on US officials to restrict their movement in Sudan.
"Any American official who comes to Sudan, we will stamp his passport for only 25km from the presidential palace," he said. "Even if they apologise and lift theirs, we will not lift ours."