African, Arab, European and U.N. leaders agreed in principle Thursday to a joint African Union and United Nations peacekeeping force for Sudan's Darfur region.

The force could be as large as 27,000 troops, including the existing 7,000-strong African Union peacekeeping force in Darfur, but the leaders did not lay out a timetable for the force to begin work partly because Sudan had some reservations.

U.N. Secretary-General Kofi Annan said additional personnel could include as many as 17,000 soldiers and 3,000 police officers.

"The next step is for the U.N. and AU to call a meeting of the non-signatories (of the Darfur Peace Agreement) ... and the government of Sudan. It should take place in the next couple of weeks to resolve outstanding issues by the end of the year," Annan said.

Enlarging the existing African Union peacekeeping force in Darfur will take place in three phases over an unspecified period of time, Annan told journalists.

Sudan has not given its unreserved approval to the plan because officials at Thursday's meeting needed to consult with their superiors in the Sudanese capital, said Abdul Mahmoud Abdelhaleem, Sudan's Ambassador to the U.N.

Some of the issues the officials could not decide on immediately included who Sudan would accept to be in command of such an expanded peacekeeping force.

An African Union Peace and Security Council meeting will be held in the Republic of Congo on Nov. 24 during which Sudan is expected to present its final views on what was agreed on in Ethiopia Thursday, Annan said.

Annan had wanted U.N. peacekeepers to replace a beleaguered AU force in Darfur. Sudan has so far blocked a U.N. contingent. Annan wanted to try to stop the bloodshed in Darfur before he leaves office on Jan. 1.

The meeting brought together senior officials from the AU, the Arab League, the European Union, Sudan, the United States, China, Russia, Egypt, France and a half-dozen African countries.

In recent days, pro-government militia known as janjaweed have stepped up attacks on villages in Darfur, killing dozens of people, international observers said Wednesday. In one raid, janjaweed militiamen — backed by government troops — forced children into a thatched hut, then set it ablaze, killing parents who tried to rescue the children, rebels said.

The U.N. humanitarian chief, who was visiting Darfur, said he had been told by people made homeless by the conflict that the withdrawal of non-governmental organizations from some areas had left them with fewer services and more exposure to violence, according to a statement released by the United Nations in New York Thursday.

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

"Aid workers in West Darfur cannot move on the roads because they are being attacked and their vehicles are being stolen," Egeland said.

After years of low-level clashes over water and land in the vast, arid Darfur region, rebels from ethnic African tribes took up arms against Sudan's Arab-dominated central government in 2003. Khartoum is accused of unleashing the janjaweed, who are blamed for many of the atrocities in a conflict that has killed some 200,000 people and chased 2.5 million from their homes.

The conflict has destabilized a wide region that includes parts of neighboring Chad and the Central African Republic. The chaos has been exploited by rebels from Sudan, Chad and the Central African Republic, and ethnic violence mirroring attacks in Darfur has been seen in Chad in recent weeks.

The Sudanese army has denied any connection to janjaweed attacks, saying the claims were politically motivated.

Some in Darfur have said the government let loose janjaweed forces in Darfur recently to put down an umbrella coalition of rebels, the National Redemption Front, which had rejected a peace deal and clashed with government forces.

The African Union said at least 30 people were killed and 40 wounded in the janjaweed raid Saturday in the north Darfur town of Sirba, and that attacks were also reported nearby.

Human Rights Watch had called for an immediate major increase in the Darfur peacekeeping force to stop the growing number of attacks on civilians.

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

The aid agency Medecins Sans Frontiers reported that thousands of people have fled their homes and refugee camps in Darfur. The agency said it was also increasingly difficult to provide aid to the victims because of the violence.