Iraqi state media initially reported that the attacks near Iraq's western border with Syria were carried out by U.S. drones, a claim that was quickly and forcefully denied by the Pentagon.

Separately, the Pentagon said that 90 additional U.S. troops arrived in Iraq, part of a group of up to 300 military advisers that President Obama said last week he would deploy there to assess the situation before taking any further U.S. military action. A statement said that U.S. aircraft are now flying 30 to 35 manned and unmanned daily surveillance flights over Iraq.

Reuters reported early Wednesday that militants had attacked one of Iraq's largest air bases, a site near the town of Yathrib that was once know as "Camp Anaconda" when U.S. troops were present. The news agency said the base had been surrounded on three sides and was under mortar fire from the militants.