The US should reimburse Iraq up to $208m for work done by a US contractor, a UN watchdog agency has said.
Halliburton denies overcharging claims
The International Advisory and Monitoring Board said the work by Halliburton had been either overpriced or insufficiently documented.
Its recommendation came after it conducted an audit on contracting work by Halliburton's KBR unit in 2003-04.
In response, the energy firm denied overcharging and insisted it had co-operated with the audit.
The IAMB has been set up to monitor the spending of Iraq's oil revenues, following the US-led invasion in 2003.
It can make recommendations but not decisions on whether reimbursements are made.
The IAMB said in a statement that it "recommends that amounts disbursed to contractors that cannot be supported as fair be reimbursed expeditiously".
It said the US government should "seek resolution with the Iraqi government concerning the use of resources of the DFI (the Development Fund for Iraq) which might be in contradiction with UN Security Council Resolution 1483".
That resolution transferred authority for expenditures from Iraq's oil revenue from the UN to the DFI.
In response, a Halliburton's spokeswoman said the agency had questioned the quality of the supporting documents for the costs, but not the costs themselves.
"Therefore, it would be completely wrong to say or imply that any of these costs that were incurred at the client's direction for its benefit are 'overcharges'," the spokeswoman, Cathy Mann, said.
Halliburton - once run by US Vice-President Dick Cheney - has previously denied allegations in the US that it overcharged for services in Iraq and enjoyed preferential access to US government contracts.