There is no end in sight for the US military occupation of Iraq and a quick exit would risk "massive chaos and even genocide," a US think tank said in a report.

The report by the Institute of Peace comes two days before US Ambassador Ryan Crocker and top commander Gen. David Petraeus are due to deliver testimony to the Congress on progress in the Iraq, now entering its sixth year.

"The US is no closer to being able to leave Iraq than it was a year ago," said the report, written by experts who advised a high-profile Iraq policy panel convened by Congress in 2006.

"Lasting political development could take five to ten years of full, unconditional US commitment to Iraq."    

The report warned that a fast exit from Iraq "risks a complete failure of the Iraqi state, massive chaos and even genocide."    

A White House spokesman was not immediately available to comment on the report.

With less than 11 months left in office and his approval ratings near the lows of his presidency, President George W Bush is trying to shore up support for sticking to his policy in Iraq, which polls show is hugely unpopular with the American public.

The institute's report said security has improved in Iraq since a "surge" in US troop levels in 2007, but gave much of the credit to Sunni fighters who turned against al Qaeda forces.

The United States has 158,000 troops in Iraq now and Petraeus is expected to tell Congress exactly how many troops will be in Iraq when current reductions are finished in July.

On Sunday, Iraqi troops backed by US forces battled gunmen in Baghdad's Sadr City in the heaviest fighting in the capital since Shi'ite cleric Moqtada al-Sadr pulled his militiamen off the streets a week ago. - Reuters