The nation's top military officer says the United States and its allies are taking every precaution to limit civilian casualties as they continue air strikes against Islamic State group militants in Syria and Iraq.

But Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said civilian casualties are inevitable in any military campaign.

"Of course you know you can't reduce it to zero," Dempsey told reporters Friday at a Pentagon news conference.

Dempsey said he has received no reports of civilian casualties so far.

Dempsey said U.S. allies participating in the campaign against Islamic State group are doing just as well their American counterparts in hitting their targets precisely.

He attributed the success to two decades of training with other countries and acquiring advanced surveillance and targeting equipment.