U.S. fighter jets and drones repeatedly bombed Sunni Islamic extremists in northern Iraq, targeting what officials described as ISIS artillery units and convoys advancing on the Kurdish regional capital of Irbil.

The airstrikes Friday ramped up America's involvement in Iraq where ISIS, which calls itself the Islamic State, is seizing control of towns and key infrastructure in an advance that has forced hundreds of thousands to run for their lives.

News of the second round of U.S. airstrikes came just after the governor of Irbil told CNN that ISIS may be as close as 30 kilometers (just over 18 miles) from the city of more than a million people.

The operation began hours after President Barack Obama authorized "targeted airstrikes," saying in a televised address late Thursday that the United States had an obligation to protect its personnel in Iraq and prevent a potential genocide of minority groups by ISIS.

Obama said there will be no buildup of U.S. combat troops in Iraq. "As commander in chief, I will not allow the United States to be dragged into fighting another war in Iraq," the President said....