In the face of imminent military assaults on key cities in Iraq and Syria, the commander of U.S. Air Forces in the Middle East said Thursday he's concerned about running low on precision-guided weapons needed for the war against the Islamic State group in both countries.

Air Force Lt. Gen. Charles Q. Brown Jr., commander of U.S. Air Forces Central Command, said the U.S. has been going through more weapons than officials forecast in the run-up to the wars. And he told Pentagon reporters that the Pentagon is looking at weapons stocks around the world.

"We have to do some analysis of where we take risk," Brown told Pentagon reporters in a videoconference from the Middle East. "And what I mean by that is, where do we pull some weapons from that we were saving for other contingencies. And do we use them now or do we save them for later?"

Brown, who oversees U.S. air operations in the Middle East, also said the Air Force is taking steps to buy more weapons but that will take time.

According to the latest Pentagon report, the U.S. has spent more than $1.7 billion on munitions in the fight against the Islamic State group since August 2014. That amounts to about $2.7 million a day.

Defense Secretary Ash Carter noted the munitions problem in February, saying there were no immediate battlefield shortages. But he noted that the Pentagon requested a significant increase in spending on munitions in the budget "partly to offset the depletion" associated with the anti-Islamic State campaign.

The U.S.-backed coalition has been conducting persistent airstrikes in both Iraq and Syria, and those could intensify as Iraqi forces move to retake Fallujah and as the Syrian Democratic Forces continue their march to defeat Islamic State fighters controlling the city of Raqqa. Both fights are in the early stages, but are expected to escalate in the coming weeks and months