In a letter addressed to Congress on Sunday, Obama said the latest airstrikes to help Iraqi forces regain control of the strategic Mosul Dam were in line with objectives to protect US interests in Iraq.

"The failure of the Mosul Dam could threaten the lives of large numbers of civilians and threaten US personnel and facilities - including the US Embassy in Baghdad," the administration wrote.

Obama added that failing to take the dam back from "Islamic State" militants could worsen the humanitarian situation, and "prevent the Iraqi government from providing critical services" to the Iraqi people.

The US military launched nine airstrikes against IS on Saturday night, and another 14 on Sunday, to clear the way for the Kurdish fighters to advance. The air attacks destroyed several armored vehicles and a checkpoint, and included the first reported use of land-based bombers in the military campaign so far.

"Mosul Dam was liberated completely," Ali Awni, an official from Iraq's main Kurdish party, told the news agency AFP on Sunday. The recapture of the facility, if confirmed, would signify a significant breakthrough in the northern Iraq campaign against IS militants, which was launched in early June.

IS fighters seized control of the dam on August 7, raising fears that they would use it as a weapon by threatening to flood as far as Iraq's capital. However, as the dam lies on the Tigris River some 50 kilometers (30 miles) north of Mosul, which is under IS control, such a move would at present prove counterproductive.

The White House said the heightened military operations seen over the weekend were undertaken in coordination with the Iraqi government and would be limited "in their nature, duration, and scope."

Two months of fighting have brought Iraq to the brink of break-up, with much of the violence concentrated in Iraqi Kurdistan. The rapid advance of IS across large swaths of the country has driven tens of thousands of minority Christians and Yazidis from their homes.

nm/tj (Reuters, AFP, AP)