The UN secretary general has said that most Middle East leaders regard the US-led invasion of Iraq and its aftermath as a disaster for the region.
Iraq has become one of the most violent places on Earth
Kofi Annan, speaking at a briefing following his recent tour of the region, said that the timing of any US withdrawal was now a key issue.
He said some leaders wanted the US to stay in Iraq and stabilise it, while others wanted an immediate withdrawal.
The White House said it disagreed with his characterisation of events in Iraq.
Spokesman Tony Snow accepted there had been unrest in Iraq but pointed to attempts to establish democracy in Lebanon and in Palestinian areas, and said democracy was also gaining a footing in Afghanistan and Iraq.
Mr Annan was speaking at a news conference at the UN in New York ahead of this year's General Assembly.
He also appealed to Iran to work with the international community to solve the dispute over its nuclear programme. Washington accuses Tehran of attempting to build a nuclear bomb.
'Cloud of uncertainty'
Speaking about his tour of Middle East nations, Mr Annan told reporters: "Most of the leaders I spoke to felt that the invasion of Iraq and its aftermath have been a real disaster for them...They believe it has destabilised the region."
But he also said many leaders wanted the Americans to stay in Iraq until the security situation improved, arguing that "having created the problem they cannot walk away".
He said other leaders, notably in Iran, felt "the presence of the US is a problem and that the US should leave, and if the US were to decide to leave, they would help them".
Mr Annan concluded: "So in a way, the US has found itself in a position where it cannot stay and it cannot leave.
"And I believe, if it has to leave, the timing has to be optimum and it has to be arranged in such a way that it does not lead to even greater disruption or violence in the region."
Turning to Iran, Mr Annan said he detected a slight shift in Tehran's approach and believed the Iranians were more open to suspending their nuclear enrichment activities as part of negotiations.
"We cannot afford another crisis in this region. I appeal to the Iranians to ...lift the cloud of uncertainty surrounding their programme, so hopefully this will be done."