U.S. warplanes on Sunday carried out four strikes on Islamic State insurgents menacing Iraq's Haditha Dam, witnesses and officials said, widening what President Barack Obama called a campaign to curb and ultimately defeat the jihadist movement.

Obama has branded Islamic State an acute threat to the West as well as to the Middle East and said that key NATO allies stand ready to back Washington in action against the well-armed sectarian force, which has seized expanses of northern Iraq and eastern Syria and declared a border-blurring religious caliphate.

The leader of a pro-Iraqi government paramilitary force in western Iraq said the airstrikes wiped out an Islamic State patrol trying to attack the dam — Iraq's second biggest hydroelectric facility that also provides millions of people with water.