The Bush administration publicly rebuked the top U.N. envoy to Sudan on Thursday, charging that he has underplayed Sudan's support for Arab militias terrorizing thousands of civilians in the province of Darfur.

John C. Danforth, the U.S. ambassador to the United Nations, said that the U.N. official, Jan Pronk of the Netherlands, is "flat-out wrong" in asserting that there is no recent evidence linking Khartoum to Arab militias rampaging through black African villages in Darfur. He cited a report Tuesday by African Union monitors in Darfur that Sudanese helicopter gunships had been used in an Aug. 26 attack on two villages.

"Any indication that the government of Sudan isn't up to its elbows in this vicious attack on innocent civilians is just plain wrong," said Danforth, noting that the attacks had been confirmed by U.S. personnel on the ground. "This is a direct military attack by the army of the government of Sudan on civilian villages in Darfur within the past week."

The rare public criticism followed a briefing by Pronk to the U.N. Security Council on a 14-page report from U.N. Secretary General Kofi Annan on Sudan's efforts to crack down on the militias and improve security in a series of camps for displaced civilians.

The report, which Pronk wrote, said Sudan has failed to stop Arab militias, known as the Janjaweed, from carrying out attacks against civilians in Darfur. But it also maintains that the government has made "some progress" in disarming the militias and increasing security for displaced civilians in some camps, a finding that diplomats say has temporarily spared Khartoum from facing a council threat of sanctions.

The crisis in Darfur began in February 2003, when two rebel groups launched an attack on Sudanese authorities, citing discrimination against the region's largely black African tribes. The United States and U.N. human rights monitors charge that Sudan responded with excessive force, sponsoring Arab militias who have killed as many as 50,000 civilians and driven more than 1 million from their homes.

Danforth pressed Sudan on Thursday to accept a U.N. proposal to send thousands of additional African troops to Darfur to monitor the treatment of civilians there. The size and mandate of such a force is the subject of Nigerian-led peace talks this week in Abuja, Nigeria, between Sudan and the two rebel groups. Sudan's U.N. ambassador, Elfatih Erwa, said his nation is willing to accept a larger African force, but not if it is given a more robust mandate to protect civilians. "We have no problem with more monitors," Erwa said. But he said Sudan would "have a problem" if African troops are given a broader mandate.

Erwa denied Danforth's charge that Sudan had engaged in offensive military operations against civilians in Darfur. He said Sudanese forces opened fired only after coming under attack by rebels.

Pronk appeared to back Sudan's account, telling the council that Khartoum had complied with an Aug. 5 agreement with the United Nations to "cease all offensive military operations in these areas, including any offensive actions against rebel groups, to exercise restraint and avoid retaliation," he said.

He noted that the African Union had told him in mid-August that "there was no evidence of attacks carried out by government airplanes" in Darfur last month. But he omitted any reference to the latest African Union report, which confirmed a Sudanese helicopter attack against the villages of Hashab and Gallab, where two Sudanese troops were killed and "13 houses were confirmed burnt." While there were no reports of civilian casualties in those incidents, the African Union also confirmed two attacks by Janjaweed militias in Klikel and Yassin, where observers discovered "a mass grave with unconfirmed 52 bodies."

Asked why he had failed to mention the latest African Union report, Pronk told reporters after the meeting that its findings were preliminary and that he is awaiting a more detailed account before determining whether Sudanese or rebel forces started the fight. "I don't think that's a final report," he said. "I don't know who was attacking whom."