The United States expressed concern Friday that the Sudanese government is not living up to obligations under the cease-fire agreement reached last week in the conflict in the western Darfur region.

The State Department is calling on Sudanese authorities to allow unimpeded access to Darfur by United Nations and other humanitarian workers, and to rein in pro-government militiamen, who are being accused of mounting continuing attacks in the area, despite the April 8 truce agreement in Chad.

The cease-fire accord calls for at least a 45-day halt to fighting between local rebels and the Arab militiamen, which has raged for more than a year, and driven nearly a million people from their homes.

At a news briefing, State Department spokesman Richard Boucher expressed concern over the Khartoum government's reported refusal to allow access to the troubled region by U.N. officials seeking to assess the extent of the humanitarian crisis there.

"We are concerned that the government of Sudan has not moved to normalize the situation in Darfur, and continues in not fully facilitating humanitarian access," he said. "That is not acceptable. We urge the government of Sudan to immediately grant visas to the two United Nations teams, who are investigating the situation in Darfur, and to other humanitarian workers who are working in Darfur."

Mr. Boucher said U.S. officials "continue to hear reports" that the government-backed militias, the so-called "Jinjaweit" have been attacking internally displaced people in Darfur.

He said the United States holds the Sudanese government responsible for stopping such attacks and reining-in the militiamen, and for protecting the civilian population.

The militiamen have done much of the fighting against the two African rebel groups that began a revolt against the Khartoum government in February of 2003, and they are accused of using scorched-earth tactics against Darfur villagers, triggering the refugee flow.

Despite press reports to the contrary, Mr. Boucher said U.S. officials expect that both rebel groups - the Sudan People's Liberation Army and the Justice and Equality Movement - will attend an African Union-sponsored meeting next week in Addis Ababa to set up a Darfur cease-fire commission.

He said the United States is urging all those involved to cooperate, so that the first monitoring mission can be sent to Darfur by the end of next week.