The assistant U.S. Secretary of State for African affairs is in Sudan's capital Saturday as part of a seven-nation tour of Africa and Europe. The official, Jendayi Frazier, told reporters on Saturday that the United States is not satisfied with the slow progress being made in ending the conflict in Sudan's western Darfur region.

U.S. envoy Jendayi Frasier told reporters that a recent upsurge in violence in Darfur is evidence of "backsliding" on the part of the Sudanese government and rebel groups in Darfur.

Ms. Frazier said the U.S. will continue to focus on solving the crisis in Darfur by providing humanitarian assistance and by pressuring the Sudanese government and Darfuri rebel groups to reach a political solution.

But she added that the U.S. wants to see action, not words, from both sides. She affirmed that U.S. sanctions on Sudan will not be lifted until its government makes visible progress toward ending the conflict.

The African Union recently accused the Sudan government of colluding with Arab militias to crush rebel forces in Darfur. Ms. Frazier says those accusations are cause for concern.

"We've seen some change and we've seen some backsliding in Darfur. With the AU force going into Darfur we saw a reduction of violence for months on end which would suggest a change in the government's behavior. Recently with the upsurge we saw the government of Sudan - the UN and other observers have said that some of the forces that have attacked communities were government of Sudan forces. So that is a reversion to actions that are unhelpful, that undermine peace," she said.

The U.S. envoy says progress in Darfur has also been hindered by divisions within the rebel factions. Some rebels this month attacked African Union peacekeeping forces, killing two AU members. Ms. Frazier stressed that rebels who attack peacekeeping forces will lose U.S. support if they continue their attacks.

The conflict in Dafur began in 2003 when rebels rose against the Khartoum government. A scorched earth campaign undertaken by government-backed Arab militias, known as janjaweed, has resulted in the deaths of an estimated 180,000 people, and displaced two million more.

Peace talks between the Sudan government and rebels in the Nigerian capital, Abuja, ended this without a firm agreement. A seventh round of talks is scheduled to begin in a month. Ms. Frazier says the U.S. hopes to see a peaceful end to the Darfur conflict by the close of this year.

The U.S. has been a major contributor, both financially and diplomatically, to Sudan. Deputy Secretary of State Robert Zoellick is scheduled to visit the country next month. It will be Mr. Zoellick's fourth trip this year.