The United Nations said it has received pledges of troops and police for a predominantly African peacekeeping force to help end the four-year conflict in Darfur that has claimed over 200,000 lives, a development that would meet a key Sudanese demand.

A large number of countries from Africa, several from Asia, one from the Middle East and none from the West were included in a preliminary list of nations that have offered military and police personnel for the 26,000-strong joint African Union-United Nations force, issued by the U.N. Peacekeeping Department and the new Department of Field Support.

"We are hitting the target of a predominantly African force, and we're very pleased about that," Assistant Secretary-General Jane Holl Lute, acting head of the Department of Field Support, said Tuesday.

The U.N. Security Council authorized the "hybrid" force a week ago after months of delay in getting agreement from the Sudanese government. It is the first joint peacekeeping operation by the African Union and the U.N. and will replace the beleaguered 7,000-strong AU force that will remain in Darfur no later than Dec. 31.

Lute, a lawyer and retired U.S. army officer who was formerly on the staff of the National Security Council, said she was pleased with the number of infantry battalions pledged at an "extraordinary" meeting last week of potential troop and police contributing countries. But she said the hybrid force still needs aviation and ground transport units.

The list of potential troop contributors includes Burkina Faso, Djibouti, Ethiopia, Egypt, Nigeria, Rwanda, Tanzania, Uganda, Bangladesh, Jordan, Malaysia, Nepal and Thailand. The list of countries offering at least 50 police officers includes Bangladesh, Burkina Faso, Ghana, Egypt, Indonesia, Nepal, Nigeria and Pakistan.

The U.N. stressed that these countries may or may not be included in the final force, which must be decided by Aug. 30 under the terms of the U.N. resolution.

In the coming months, the United Nations will beef up the African Union force, deploying personnel and equipment for command and control immediately, establishing a headquarters by October, and replacing the AU force with the joint operation by Dec. 31.

"The clock is ticking and there are expectations," Lute told a news conference. "So this will translate into people on the ground, capabilities on the ground, and resources on the ground in sufficient numbers to meet credibly the benchmarks that have been established by the council."

The AU-U.N. force will be highly mobile and dynamic, with "robust" rules of engagement so it can protect civilians and facilitate the delivery of humanitarian aid, she said.

The hybrid mission — which will also include between 4,700 and 5,000 civilians — will cost more than $2 billion annually once it is fully deployed, Lute said.

While the Security Council urged speedy deployment, the bulk of the force is not expected to be on the ground until next year.

Lute stressed that "continuing support of the government of Sudan will be necessary for smooth transition" from the African Union to the hybrid operation.

After stalling for months, Sudanese President Omar al-Bashir agreed in April to a "heavy support package" to strengthen the AU force, including 3,000 U.N. troops, police and civilian personnel, along with aircraft and other equipment.

Lute said key elements of the package will be deployed in September and October.

In June, the Sudanese government agreed to the hybrid operation, on condition it was predominantly African. Al-Bashir had wanted AU troops to remain in Darfur, arguing that U.N. peacekeepers would represent a foreign occupation and intervention, and remind the country of its colonial past.

But the poorly equipped and underfunded AU force has been unable to stop the fighting, and neither has the Darfur Peace Agreement, signed a year ago by the government and one rebel group. Other rebel factions called the deal insufficient.

The U.N. and AU are now engaged in a major effort to get all combatants to negotiate a settlement of the conflict which began in 2003 when rebels took up arms against the Sudanese government, accusing it of decades of neglect. Sudan's government is accused of unleashing in response a militia of Arab nomads known as the janjaweed — a charge it denies.