The US military cannot account for 190,000 AK-47 assault rifles and pistols given to the Iraqi security forces, an official US report says.
AK-47 assault rifles might have ended up in insurgents' hands
The Government Accountability Office (GAO) says the Pentagon cannot track about 30% of the weapons distributed in Iraq over the past three years.
The Pentagon did not dispute the figures, but said it was reviewing arms deliveries procedures.
About $19.2bn has been spent by the US since 2003 on Iraqi security forces.
GAO, the investigative arm of the US Congress, said at least $2.8bn of this money was used to buy and deliver weapons and other equipment.
Correspondents say it is now feared many of the weapons are being used against US forces on the ground in Iraq.
The Iraqi interior ministry has blamed the Americans for the disappearance of the weapons.
A spokesman, Brigadier General Abd-al-Karim Khalaf, told the BBC his ministry had not been consulted over the distribution. He also said there was no evidence to suggest that insurgents might have got hold of some of the weapons.
The GAO said weapons distribution was haphazard and rushed and failed to follow established procedures, particularly from 2004 to 2005.
MISSING IN IRAQ
AK-47 rifles: 110,000
Body armour pieces: 135,000
During this period, security training was led by Gen David Petraeus, who now commands all US forces in Iraq.
The GAO reached the estimate - 111,000 missing AK-47s and 80,000 missing pistols - by comparing the property records of the Multi-National Security Transition Command for Iraq against records maintained by Gen Petraeus of the arms and equipment he ordered.
Deputy Assistant Defence Secretary Mark Kimmitt told AFP the Pentagon was "reviewing policies and procedures to ensure US-funded equipment reaches the intended Iraqi security forces under the Iraq program".
The report comes as a political battle rages in Washington over the progress of the war in Iraq.
Gen Petraeus and US Ambassador to Iraq Ryan Crocker are scheduled to report to Congress by mid-September on the success of efforts to halt sectarian violence and return Iraq to viable self-governance.
Meanwhile, at the end of July, the US Defence Department admitted that the US-led coalition in Iraq had failed to deliver nearly two-thirds of the equipment it promised to Iraq's army.
The Pentagon said only 14.5m of the nearly 40m items of equipment ordered by the Iraqi army had been provided.
The US military commander in charge of training in Iraq has asked for help in speeding up the transfer of equipment.
Iraq's ambassador to the US said the delays were hindering the fighting capacity of its armed forces.