Nine billion dollars "from the sale of Iraqi oil and gas, and some frozen Saddam Hussein-era assets" should have been in "a special fund administered by the US Department of Defense, the Development Fund for Iraq (DFI), and was earmarked for reconstruction projects.
But the report says that a lack of proper accounting and poor oversight makes it impossible to say exactly what happened to most of it.
According to the report, the Pentagon is unable to fully account for $8.7bn of funds it withdrew between 2004 and 2007..."
This is not the first time that allegations of missing billions have surfaced in relation to the US-led invasion of Iraq and its aftermath.
In 2005, the inspector general criticised the Coalition Provisional Authority, the US-led occupation administration, for its management of an $8.8bn fund that belonged to the Iraqi government.
A criminal investigation conducted led to the conviction of eight US officials on bribery, fraud and money-laundering charges.