Sudan reversed its long-standing opposition to welcome United Nations support for the African Union peacekeeping mission in Darfur, one of the world's bloodiest conflict zones.

"It is agreed in principle that, pending clarification of the size of the force, we should be able to take it forward," UN Secretary-General Kofi Annan said late on Thursday at the end of a major diplomatic meeting on Darfur in Addis Ababa.

"The troops should be sourced from Africa as far as possible and the command and control structure would be provided by the UN," he said, adding the force would include as many as 17,000 troops and 3,000 police.

The outgoing UN chief convened the meeting between Sudanese officials and African Union, Arab League, European Union and UN leaders in an attempt to end bloodshed in the vast Sudanese region.

Sudanese diplomats said Thursday they needed to consult with their superiors in Khartoum before giving unreserved support to the plan.

But it was clear there were still disagreements over the size and shape of the force.

The leaders did not pinpoint a timetable for the force to start work partly because Sudan had some uncertainties, including the question of who would be in command.

Sudan's UN ambassador Abdalmahmood Abdalhaleem Mohamad told reporters after the meeting that the peacekeepers will be African while the UN would provide the logistical support.

"If you have a predominantly African force, then you expect to it to be led by an African commander," he said.

He also expressed reservations over the size of the force.

"The UN says 17,000 (troops), that figure is very high. We think 11,000 to 12,000."

Sudan is expected to respond to the latest proposal before the AU Peace and Security Council meets on Nov. 24 to discuss Darfur.

The AU force mandate expires on Dec. 31.

The UN Security Council voted in August to replace the AU's underpowered force of 7,000 troops with 20,000 U.N. peacekeepers.

But Sudanese President Omar al-Bashir repeatedly rejected their deployment, and this paved the way for new proposals for a "hybrid" alternative in which the United Nations would boost the AU force.

In recent days, pro-government militia forces known as janjaweed have ramped up attacks in Darfur villages, killing dozens of people, international observers said Wednesday.

In one raid, rebels described seeing janjaweed militiamen force children into a thatched hut, then set it on fire, killing parents who tried to rescue the children.

Human Rights Watch has called for a significant increase in the size of the Darfur peacekeeping force.

The New York-based advocacy group said it has documented renewed aerial bombing attacks on civilians both in Darfur and inside neighboring Chad since late last month.

The aid agency Doctors Without Borders, or Medecins Sans Frontieres, also reported that thousands of people have fled their homes and refugee camps in Darfur.

The agency warned that it was becoming increasingly difficult to provide aid to the victims because of the violence.

The gravity of the conflict was underscored on Thursday when UN humanitarian chief Jan Egeland cut short a planned three-day trip to Darfur after government officials warned the areas he wanted to visit were too dangerous.

"This is my fourth visit to Darfur, and I have never before seen such a bad security situation," Jan Egeland said from El Geneina, capital of West Darfur.

"There are too many armed elements in and around the camps threatening the inhabitants and preventing us from going in."

Egeland said aid workers in West Darfur were prevented from travelling on roads because they were being attacked.

After years of low-level clashes over water and land, rebels from ethnic African tribes took up arms against Sudan's Arab-dominated central government in 2003.

Khartoum is accused of unleashing the janjaweed militiamen, who are blamed for the atrocities in a conflict that has killed some 200,000 people and driven 2.5 million from their homes.

The Sudanese army has dismissed the accusations, saying the charges are politically motivated.

The conflict has been exploited by rebels from Sudan, Chad and the Central African Republic, and ethnic violence mirroring attacks in Darfur has travelled beyond Sudan's borders into both Chad and Central African Republic in recent weeks.

With files from The Associated Press