The Pentagon says U.S. military operations against Islamic State militants in Iraq are costing, on average, $7.5 million per day.
Rear Admiral John Kirby said Friday the cost in Iraq has increased as activities have intensified since they started in mid-June.
The news comes a day after President Barack Obama downplayed the possibility of adding U.S. airstrikes against Islamic extremists in Syria, but added the administration is still working on a comprehensive plan to deal with the terrorist group.
Kirby says the military is in the process of drawing up options for the president to potentially order strikes on Islamic State targets in Syria as they have done in Iraq.
"The Syria component is relatively new. We continue to refine and work on options - that's our job, but that doesn't mean that while you have planners doing that at a low level, that you're ready at a high level to sit down and examine them in great detail," he said. "And we just aren't there yet as an interagency team."
The U.S. has conducted more than 100 airstrikes in Iraq, most of them around the Mosul Dam facilities. U.S. air strikes helped Iraqi and Kurdish forces retake the facilities earlier this month, and Kirby says the U.S. will continue strikes as long as Islamic State militants keep trying to threaten the facilities.
Calls have mounted for greater U.S. intervention as extremist militants continue a campaign that UN officials have said amounts to ethnic and religious cleansing.
The group has released bloody execution videos, including one showing the beheading of American journalist James Foley. It has threatened to carry out more beheadings if the U.S. does not stop its airstrikes in Iraq.
UN chief Ban Ki-Moon on Friday again expressed outrage at the group's "brutal killings of civilians." Ban said whole communities that had lived for generations in northern Iraq are being force to flee or face death just for their religious beliefs.
Syria said this week it would welcome U.S. and British help in fighting the militants, but only in coordination with Damascus. It says a unilateral U.S. attack would violate its airspace and could lead to an attempt to shoot down American warplanes.
U.S. officials say they would not first consult Syria, saying President Bashar al-Assad has lost the authority to lead.