The audit of 15 noncompetitive contracts paid for by US government agencies with Iraqi oil money was unable to account for $22.4 million in funds, a UN-led watchdog said on Monday.
The audit by KPMG, ordered by the International Advisory and Monitoring Board (IAMB), said that in some cases Iraq did not receive goods and there were "unreconciled payments".
The report also said there was no evidence that steps were taken to fix previously reported problems with corruption.
The contracts varied from paying for guards for oil pipelines to training Iraqi police and military to the purchase of vehicles and food.
"In view of these findings, the IAMB recommends that the Iraqi government seek resolution with the US government concerning the use of resources of the [Development Fund for Iraq], which might be in contradiction with the UN Security Council Resolution 1483," the board said in a statement posted on its website.
The IAMB, which also includes officials from the World Bank and International Monetary Fund, was created by the UN Security Council in 2003 to oversee the use of Iraqi oil money while the country was under an interim US administration.
The watchdog's mandate expires at the end of December.
In 2004 an audit, ordered by the Coalition Provisional Authority (CPA) which governed Iraq after the US-led invasion, found that more than $8.8bn of Iraqi money was missing.
The CPA found that the money had been paid for goods and services that were never provided.
The US hoped Iraq would become a model for the Arab world
In other cases, millions of dollars were paid by the CPA in salaries for thousands of security guards who did not exist.
In other cases the money simply vanished.
Since the CPA handed over the power to Iraqis, corruption has become even worse.
A new survey released yesterday by Transparency International, an anti-corruption watchdog, ranked Iraq as the second most corrupt country in the world.
The 2006, Corruption Perception Index placed Iraq in joint 162nd place - tied with Myanmar and Guinea - but marginally ahead of Haiti, the world's most corrupt nation.