U.S. military aircraft have launched a "targeted" airstrike against Islamic militants in Iraq, the Pentagon said Friday. 

The strike comes after President Obama announced late Thursday that he has authorized limited military action to defend American personnel in the region and to protect civilians stuck on a mountain outside the city of Sinjar. 

The Pentagon said the military conducted the strike at 6:45 a.m. ET, against terrorists with the Islamic State (IS), the group formerly known as ISIS. 

Two F-18 aircraft dropped "500-pound laser-guided bombs on a mobile artillery piece" near the city of Irbil, after IS was using the artillery to shell Kurdish forces defending the city where U.S. personnel are located, the Pentagon said.