The United States has urged the United Nations to get 3,600 new peacekeepers on the ground in conflict-wracked Darfur by June, according to a letter obtained Tuesday by The Associated Press.

Ambassador Richard Williamson, the U.S. special envoy to Sudan, told Secretary-General Ban Ki-moon in the letter that additional troops are the best hope of increasing security in the Sudanese region.

A joint African Union-United Nations peacekeeping force took over in January from a beleaguered AU force to try to stem the violence. But it only has about 9,000 troops and police on the ground, out of a total of 26,000 that have been authorized.

"We believe that the deployment of 3,600 new African troops by June - a target number based on the U.N.'s planning schedule - will bring increased security and stability to the people of Darfur," Williamson wrote.

"At this crucial moment, the deployment of new troops as quickly as possible is our best hope to change the course of this tragedy."

The U.N. believes that far more than 200,000 people have been killed in the conflict. Fighting has raged in Darfur since 2003, when ethnic African tribesman took up arms, complaining of decades of neglect and discrimination by the Sudanese Arab-dominated government. Khartoum has been accused of unleashing janjaweed militia forces to commit atrocities against ethnic African communities in the fight with rebel groups.

Williamson said the United States has committed $100 million to train and equip African peacekeepers pledged to deploy as part of the AU-U.N. force, "and we will work to assist troop contributing countries in meeting the U.N. deployment schedule."

The U.S. wants Egyptian, Ethiopian and Rwandan contingents in Darfur by June, Williamson said. He noted that the Ethiopians and Rwandans are already participating in U.S.-sponsored training prior to their deployment.

While the U.S. supports the U.N. objective of deploying the best-equipped troops possible, Williamson said, "it seems that some U.N. practices may hinder deployment."

He explained in a telephone interview that the United Nations normally requires that a peacekeeping battalion be able to sustain itself by having its own equipment, the ability to maintain it, and to maintain the camps for troops.

The United States will continue to help troops from contributing countries to become self-sustaining, Williamson said, but in the meantime the U.S. wants the U.N. to provide short-term maintenance and support for the peacekeepers.

"Our point is that they have $1.28 billion just for UNAMID, and they've spent only a fraction of it and the fiscal year is going to end" in June, Williamson said, using the initials of the AU-U.N. force.

"So 75 percent of the year's gone by and we're told they've spent just 25 percent. Yet, they don't have the capacity to absorb troops at the rate they can be made available," he said.

Williamson said the AU-U.N. force only added 290 peacekeepers since Jan. 1 "and that is just unacceptable for the people of Darfur who are suffering."

"Peacekeepers on the ground are one of the tangible ways we can change the dynamic in Darfur," he said.

If all African troops that have been pledged were deployed, there could be 18,000 troops in Darfur by the end of the year, he said.

At Sudan's insistence, the U.N. Security Council agreed that the force would be predominantly African.

Williamson said the Sudanese government also continues to raise impediments to deployment of the force. He said the U.S. and other countries that are "friends" of the AU-U.N. force are trying to deal with the government of Sudan to solve them.