Jan Pronk said an ethnic cleansing campaign in 2003 and 2004 had been successful and a larger, more sophisticated and mobile force was needed to help end the continuing rapes and killings and stop the groups of 500 to 1,000 militia on camel and horseback that still attack villages at least once a month.

"Looking back at three years of killings and cleansing in Darfur we must admit that our peace strategy so far has failed," he told the U.N. Security Council. "All we did was picking up the pieces and muddling through, doing too little too late."

Decades of low-level tribal clashes over land and water in the vast western Darfur region erupted into large-scale violence in early 2003 when ethnic African tribes took up arms, accusing the Arab-dominated central government of neglect.

The government is accused of responding by unleashing Arab tribal militias known as Janjaweed to murder and rape civilians and lay waste to villages. It denies the charge.

An estimated 180,000 people have died in the upheaval, many from hunger and disease.

Pronk briefed the council a day after the African Union's Peace and Security Council accepted in principle the need to transform its 7,000-strong peacekeeping force in Darfur into a U.N. peacekeeping force.

The AU council extended the AU force's mandate until March 31, authorized consultations with the U.N., and said a final decision would be taken by ministers at the end of March, Tanzania's U.N. Ambassador Augustine Mahiga told reporters.

The AU force has made a significant difference where its troops have been deployed. But it has been hampered by a shortage of funds, troops, and equipment and its mandate has been limited to monitoring an April 2004 cease-fire that is regularly broken by all parties and offering limited protection to civilians.

Pronk said a new type of force with sophisticated military hardware and air surveillance is needed to disarm militias, help stop attacks, and deploy to villages so the 2.2 million people who fled the violence and now live in camps can return to their homes.

"People don't go home if they are uncertain, unless there are reliable people to protect them," he said.

Pronk said he envisions a U.N. force of at least 12,000 to 20,000 troops.

But a U.N. force could face problems from the Sudanese government, which has opposed non-African peacekeepers.

Sudan's charge d'affaires Yasir Abdelsalam told reporters that "the African Union is doing well" and Pronk commended its work. "This is why we think the African Union should be given more support to succeed," he said.

Tanzania's Mahiga, the current council president, told reporters the Security Council hopes that negotiations between the government and rebels on a peace agreement in Darfur will be completed before a U.N. force deploys.

Both the AU and the Security Council must authorize the hand over and no date has been set.

Meanwhile, Sudan's bid to chair the African Union has been called into question because of the country's poor human rights record and the conflict in Darfur.

By tradition, Sudan's President Omar El-Bashir should become the next chairman of the 53-nation regional group at its upcoming summit in the Sudanese capital, Khartoum, on Jan. 23-24.

But Tanzania's U.N. Ambassador Augustine Mahiga, the current Security Council president, said Friday that no decision has been made.

Asked whether Sudan should chair the AU under these circumstances, Mahiga said, "It would create difficulties, and I think the consultations will take into account those difficulties."

Chadian President Idriss Deby has accused Sudan of backing rebels who are seeking to overthrow his government. He has called on the AU to block Sudan from taking over the AU president because of its aggressive attitude toward its people and toward Chad.