In a toughly worded report, Secretary-General Kofi Annan on Monday urged the US to quickly restore control to Iraqis and warned that "democracy cannot be imposed from the outside."
In the 23-page report to the Security Council, Annan also noted concerns regarding the US treatment of Iraqi detainees and the failure to improve security conditions in Baghdad.
Annan welcomed the creation of a US-picked Iraqi Governing Council, though he wrote that Iraqis were feeling "an overwhelming demand for self-rule."
"It is important that Iraqis are able to see a clear timetable leading to the full restoration of sovereignty," Annan wrote.
The critical tone of the report was unlikely to help US efforts to win support for an international peacekeeping force that could ease overburdened American troops in Iraq.
Still, US diplomats offered an initially positive reaction to Annan's report.
"We certainly agree that Iraqis should be in charge of their own country and we are working hard to do that and that's why the governing council is a good first step," said Richard Grenell, spokesman for the US mission to the UN.
Annan was softer on the Americans when he spoke with reporters Monday, ahead of a meeting with US Ambassador John Negroponte.
"I think, given the circumstances, and the fact that you couldn't possibly organize elections in Iraq today, it was a good method of putting together a council and I hope the Security Council will see it that way and grant the group its support," Annan said.
Annan's report was made public a day ahead of a Security Council meeting on Iraq to be attended by him, his special envoy to Iraq Sergio Vieira de Mello and three members of the Governing Council.
The delegation will include Ahmed Chalabi -- once favored by US defense officials to be Iraq's next president -- as well as Adnan Pachachi, a former Iraqi vice president, and Akila Hashami of the Iraqi Foreign Ministry.
The Governing Council, the first civilian group organized to eventually take control of Iraq, plans to declare itself the sovereign representative of Iraq at the UN.
Such a move could satisfy potential peacekeeping donors such as France and India who are reluctant to send forces while the US and Britain remain solely in charge.
The Iraqi Governing Council will be able to pick ministers for a new administration and hold other powers, but the final say will remain with US administrators.
Annan wrote that it was important to achieve "Iraqi ownership of the political process."
The report offers UN help to Iraqis in defining the priorities and policies that will shape the future of the country. Throughout the report, Annan emphasizes the importance of Iraqi sovereignty.
"There is an overwhelming demand for self-rule and democracy cannot be imposed from the outside," he wrote.
Much of the report is based on Vieira de Mello's observations and discussions with US officials in Baghdad, including L. Paul Bremer, the US occupation governor for Iraq.
Last week, Viera de Mello complained to Bremer about the "treatment of detainees and the conditions under which they were held in detention," Annan wrote.
The report also expresses concerns about living conditions and "precarious security situation" in Baghdad, which was been plagued by crime and sabotage.
Annan also offered the US assistance in such areas including demining and police training. But Annan ruled out the possibility of a UN police force working side-by-side with US troops.