The US ambassador to Iraq has said that continuing sectarian violence there had the potential to turn into civil war.
Holy sites in Iraq are being protected after recent attacks
In an interview with the Los Angeles Times, Zalmay Khalilzad indicated that the US had little choice but to keep a strong military presence in Iraq.
He added that the dangers of conflict would be lessened if Iraqis agreed on a national unity government.
But US Defence Secretary Donald Rumsfeld said the media had exaggerated the severity of recent violence.
At a Pentagon briefing, Mr Rumsfeld also said there had always been the potential for civil war in Iraq.
Mr Khalilzad told the American newspaper, that the US-led invasion in 2003 had opened "the Pandora's box" of tensions in Iraq.
"The way forward, in my view, is an effort to build bridges across [Iraq's] communities," he said.
The envoy said that a continuing political stalemate over who should be the new prime minister in Iraq's first full-term government was complicating effort to form a broad-based cabinet.
Mr Khalilzad added that although the threat posed by the bombing of a Shia mosque in Samarra last month had now passed, Iraq remained vulnerable to insurgents' attempts to exploit political uncertainty.
"There is a concerted effort to provoke civil war," he said.
Mr Khalilzad warned that if the region erupted into sectarian conflict that "would make Taleban Afghanistan look like child's play".
At the Washington briefing, Mr Rumsfeld said he did not believe a civil war was going on in Iraq, although admitted that such danger remained.
He said Iraq "was held together not by a constitution, not by a piece of paper, not by respect for the fellow citizens of different religious faiths, but it was held together through force and viciousness".
"And that's gone," Mr Rumsfeld said.
He also went on to attack the quality of reporting from Iraq, saying that much of it - both in the US and abroad - had exaggerated the situation.
Mr Rumsfeld also said Iranian forces had infiltrated Iraq - something, he said, they would look back on as being an error of judgement.