The US has launched airstrikes around Haditha Dam, targeting Islamic State (IS) militants in the area for the first time.
IS, which is also known as ISIS or ISIL, is trying to capture the vital dam in the west of the country.
US officials say that while Anbar Province remains in control of the Iraqis, the offensive is an effort to push back fighters who have been trying to take over dams across the country.
Pentagon spokesman John Kirby said: “At the request of the Government of Iraq, the US military today conducted coordinated air strikes against Islamic State of Iraq and the Levant (ISIL) terrorists in the vicinity of the Haditha Dam in Anbar province.
“We conducted these strikes to prevent terrorists from further threatening the security of the dam, which remains under control of Iraqi Security Forces, with support from Sunni tribes.”
US Defense Secretary Chuck Hagel said the four airstrikes had been carried out at the request of the Iraqi government.
He said: “If that dam would fall into ISIL’s hands or if that dam would be destroyed, the damage that that would cause would be very significant and it would put a significant, additional and big risk into the mix in Iraq.”
Sheik Ahmed Abu Risha, the leader of a pro-Iraqi government paramilitary force said the strikes were “very accurate”.
He said: “There was no collateral damage … If Islamic State had gained control of the dam, many areas of Iraq would have been seriously threatened, even Baghdad.”
It is Washington’s first offensive in Anbar province since it started hitting IS forces in the north of the country in August.
Since then the US has conducted more than 130 airstrikes.
IS fighters tried to capture Haditha Dam, which has six power generators located alongside the country’s second largest reservoir, last month.
Iraqi forces supported by Sunni tribes held them off.
IS took control of the Mosul Dam in northern Iraq last month, but US airstrikeshelped to dislodge them.
The militants seized a dam outside Falluja in April and flooded areas on the rural outskirts of western Baghdad, forcing thousands of people to leave their homes.
IS has overrun large areas of northern Iraq and declared a cross-border Islamic caliphate (state), including territory it controls in neighbouring Syria.
Iraq’s government has meanwhile welcomed US President Barack Obama’s plan for an international coalition against the jihadists, calling it a “strong message of support”.
Mr Obama outlined the plan at this week’s Nato summit, amid growing international concern about IS.