The United States condemned on Monday the killings of two African Union peacekeepers in Sudan's Darfur region and demanded that the Sudanese government cooperate with the peacekeepers.

A State Department spokesman also said work is continuing urgently at the United Nations to constitute a stronger force to relieve the AU soldiers.

Two African Union soldiers were killed and three wounded in an ambush by unidentified fighters Saturday in the vast desert area wracked with violence for more than three years. More than 200,000 people have died, and 2 million have been put to flight by the warfare.

"We call on the Sudanese government to cooperate fully with AMIS, to arrest those who participated in the attack and prosecute them," said acting spokesman Gonzalo R. Gallego, using the acronym for the African Union Mission in Sudan.

"We also call upon all groups in Darfur to refrain from violent attacks, recognize their responsibilities and abide by the Darfur Peace Agreement and the N'Djamena cease-fire agreement." N'Djamena is the capital of neighboring Chad.

The peace agreement, negotiated in Abuja, Nigeria, was signed in May by President Omar el-Bashir's mainly Arab government and the largest of several black African rebel groups in Darfur. Once implemented, it would establish an autonomous Darfur headed by Minni Minnawi, the rebel leader who signed the agreement.

The killing has continued unabated. The United States and Britain are pressing for passage of a U.N. Security Council resolution to convert the 7,000-strong African Union force to U.N. sponsorship and expand it to about 22,600 soldiers and police.

President George W. Bush is demanding that the U.N. force be in place by Oct. 1.

Gallego demanded that the Sudanese government cooperate to enable the transition.

"We are working with our international partners at the U.N. Security Council to finalize the resolution for the U.N. peacekeeping force in Darfur, consistent with the African Unions request," Gallego said.

"The UN force must deploy without delay. Only a large, mobile, fast-reacting and robust U.N. force" can be expected to succeed, he said.