About $2.2 billion from the fund has been used in the past month to meet rising fuel prices and to buy protective gear for the force, including body armour, armoured Humvees and aircraft survivability equipment, said Lieutenant-Colonel Rose-Ann Lynch on Wednesday.
"The department is executing these funds just as Congress expects us to," she said.
President George Bush's administration had said it would not need the emergency funds for Iraq this fiscal year, but Congress went ahead and passed legislation anyway creating the $25-billion emergency fund and making it available immediately.
The cost of the war in Iraq through June averaged $4.4 billion a month, according to Pentagon figures. In Afghanistan, the United States has spent another $775 million a month on average this fiscal year to June.
Increased number of attacks
But the pace of military operations has stepped up since June in the face of rising attacks as both countries head into violently contested elections.
In April, the last time violence spiked in Iraq, war costs surged to $5.2 billion.
In addition, plans for another major rotation of US forces in Iraq this year at a time of soaring fuel prices will add to the bill.
Lynch said the $25-billion emergency fund will cover war costs until Congress approves additional funding for Iraq and Afghanistan.
That is on top of a $416 billion defence budget for fiscal year 2005.