US-led coalition air strikes against ISIS started last August, and have poured about 2.7 billion US dollars into the fight, and by the rate of 9 million per day.
Two-thirds of the total bill has gone to the Air Force, US Congress rejected legislation banning further spending. The US House of Representative approved a $579 billion of defence spending bill.
An amendment calling to halt cash flowing to fight ISIS was rejected, unless Congress passed a new authorisation for the use of force.
This week, the White House announced another 450 advisers for Iraq, bringing the total military personnel to 3,500.
General Martin Dempsey, chairman of the US Joint Chiefs of Staff, said his country's’ presence in Iraq may expand, and more US bases built in Iraq remained a future option, following the model of the Taqaddum air base in Anbar province.
These comments came one day after the Obama administration announced it is going to deploy 450 troops to be stationed at the airbase.