The United States is urging the United Nations to get 3,600 new troops on the ground in Darfur by June.

Ambassador Richard Williamson, the U.S. special envoy to Sudan, says the additional troops are the best hope of increasing security in the conflict-wracked Sudanese region.

Williamson wrote to U.N. Secretary-General Ban Ki-moon encouraging the United Nations to speed up the deployment. His letter was obtained Tuesday by the Associated Press.

A joint United Nations-African Union peacekeeping force was launched in January 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.