US strikes Islamic State militants at Iraq's Haditha dam
The US has carried out a series of air strikes on Islamic State militants close to the vital Haditha dam in Iraq's western Anbar province.
The US strikes, the first in the area, were to protect the Iraqi forces and Sunni tribesmen in control of the dam.
The governor of Anbar has been lightly wounded in fighting in the province, the army has said.
Separately, US President Barack Obama said he would set out a plan of action against IS in a speech on Wednesday.
Mr Obama had been much criticised for saying "we don't have a strategy yet" when asked about IS during a press conference last month.
Analysis: Jim Muir, BBC News, northern Iraq
The American air attacks, the first of their kind in Anbar province, signal that Washington has crossed a line that it itself drew.
It has long had a standing request from the outgoing Iraqi government to use its air power against IS in all areas. But until recently, it made it clear it would only do that once a new, inclusive government is formed in Baghdad, with full Sunni representation.
That hasn't yet happened, though intensive efforts are under way to produce a new cabinet in the coming days.
The US has carried out more than 130 air strikes since early August to support Iraqi and Kurdish forces fighting IS in northern Iraq, but these were the first in Anbar.
A US official said: "At the request of the Iraqi government and in keeping with our mission to protect US personnel and facilities, US military planes have begun striking Isil terrorists near the Haditha dam."
The Pentagon's press secretary, Rear Admiral John Kirby, later said: "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."
The Iraqi army said a mortar round had lightly wounded Governor Ahmed al-Dulaimi in the town of Barwana shortly after it was retaken from IS on Sunday. He was hit in the head by shrapnel.
IS, also often referred to as Isil or Isis, has taken over large swathes of Iraq and Syria in recent months, declaring the land it holds a "caliphate".
Islamic State fighters have targeted a number of dams in their offensive, capturing the facility at Fallujah.
They also took the largest dam, at Mosul, but US air strikes helped force them out.
The group has so far failed in its attempts to capture Haditha dam, on the Euphrates valley in western Anbar province. It is Iraq's second largest dam.
IS militants in August reportedly closed eight of the Fallujah dam's 10 lock gates that control the river flow, flooding land up the Euphrates river and reducing water levels in Iraq's southern provinces, through which the river passes.
Many families were forced from their homes and troops were prevented from deploying, Iraqi security officials said.
IS also controls other key national assets - several oil and gas fields in western Iraq and Syria.
Kurdish forces in northern Iraq earlier recaptured the strategically important Mt Zartak, which overlooks a plain that stretches to Mosul, the city seized by IS in June.
The mountain fell to the Islamists last month when they staged a lightning attack on Iraqi Kurdistan.
Since then Kurdish "peshmerga" fighters have been slowly pushing back, assisted by US air power.
The BBC's Jim Muir in Iraq says Mount Zartak was retaken in a short, sharp battle that left more than 30 IS fighters dead.