Iraq's parliament is chasing about $17bn of Iraqi oil money it says was stolen after the 2003 US-led invasion and has asked the United Nations for help to track it down.
The missing money was shipped to Iraq from the United States to help with reconstruction after the ouster of Saddam Hussein.
In a letter to the UN office in Baghdad last month, parliament's Integrity Committee asked for help to find and recover the oil money taken from the Development Fund of Iraq (DFI) in 2004 and lost in the chaos that followed the invasion.
"All indications are that the institutions of the United States of America committed financial corruption by stealing the money of the Iraqi people, which was allocated to develop Iraq, (and) that it was about $17bn," said the letter sent to the UN with a 50-page report.
The committee called the disappearance of the money a "financial crime" but said UN Security Council resolutions prevent Iraq from making a claim against the United States.
"Our committee decided to send this issue to you ... to look into it and restore the stolen money," said the letter.
UN officials were not immediately available for comment.
The DFI was established in 2003 at the request of the Coalition Provisional Authority (CPA), the US body headed by Paul Bremer that governed Iraq after the invasion. The fund was to be used to pay the salaries and pensions of Iraqi government workers and for reconstruction projects.
In 2004, the administration of former US President George W. Bush flew billions of dollars in cash into Iraq. The money came from the sale of Iraqi oil, surplus funds from the UN oil-for-food program and seized Iraqi assets.
Last July, an audit report from the US Special Inspector General for Iraq Reconstruction (SIGIR) said the US Department of Defense was unable to account properly for $8.7bn of Iraqi oil and gas money after the 2003 invasion.
Iraqi government spokesman Ali al-Dabbagh told Al Jazeera television on Sunday: "No one on the Iraqi side was controlling the work of Paul Bremer at that time. So I think the administration of the United States needs to give the answers for where and how this [money] was being used.
"We do understand that Iraqis are also engaged in such lack of transparency and corruption related to the Paul Bremer time in Iraq," he added.
Osama al-Nujaifi, Iraq's parliament speaker, said a committee was investigating what happened to some $20bn of DFI money.
"Some of these funds were spent and are documented. But some do not have such documents," he said. "We as a parliament are working together with the Iraqi Board of Supreme Audits and with coordination of SIGIR to know where this money ended up."
The appeal to the United Nations could help Iraq recover its money by putting its case before the international community, said Bahaa al-Araji, the head of the Integrity Committee.
"We cannot sue the Americans. Laws do not allow us to do that. All we want is to get this issue to the UN," Araji said. "If this works, it will open the way for Iraq to restore its stolen money."
In 2003, the CPA issued an order granting immunity to US personnel and institutions working in Iraq.