The United States has spent more than $2.7 billion on the military campaign against the ISIL terrorist group in Iraq and Syria, averaging more than $9 million a day, the Pentagon says.

The US Air Force has borne two-thirds of the total spending, or more than $1.8 billion, since President Barack Obama ordered airstrikes against ISIL last August, the Department of Defense said Thursday in its first breakdown of the operation's costs.

The daily combat, reconnaissance and other flights use up more than $5 million a day, the Associated Press (AP) reported.

Operation costs rose from an average of $5.6 million a day to $9.7 million a day in mid-September, when US airstrikes expanded from Iraq into neighboring Syria.

War spending continued to average around that figure through late May.

Other costs include $438 million for the Navy, $274 million for the Army, $16 million for military pay, and $646 million was spent on munitions.

Smoke rises from the Syrian city of Kobani, following airstrikes by the US-led coalition, Nov. 17, 2014. (AP photo)

The Pentagon’s announcement follows the Obama administration’s decision to send an additional 450 military personnel to Iraq to support Iraqi security forces battling ISIL militants.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said Thursday that the administration is considering establishing additional military bases in Iraq.

The top general said a new military base, being established in Anbar Province, could be a model for more such US military hubs across Iraq.

Recent setbacks in Iraq and Syria, which have seen some territory falling into the hands of ISIL forces, have raised serious doubts about Obama’s strategy against the brutal group.

Early in the week, Obama told a G7 summit in Germany that “we don’t yet have a complete strategy” against ISIL.

HRJ/HRJ