Kurdish fighters supported by Iraqi military and US airstrikes have recaptured Iraq's largest dam, which had been under control of militants from the Islamic State, according to Iraq state media reports.

Military spokesman Lt-Gen Qassim Atta told state TV that the dam had been "fully cleansed" on Monday, although some reports said that fighting was ongoing in the area surrounding the dam.

Ground troops were supported by a joint air patrol, he added, without saying if there had been more US airstrikes.

Iraqi military officials said on Monday that security forces had recaptured the facility, after days of fighting in the surrounding areas, bolstered by US airstrikes.

Mosul dam has been at the centre of fierce fighting since militants from the Islamic State grabbed large swathes of land in northern Iraq in June, including the country's second city of Mosul

The ultra-violent jihadist group has declared the establishment of an Islamic Caliphate across the territory it controls in eastern Syria, as well as parts of Iraq.

Whoever controls the Mosul dam controls water and electricity supplies for much of northern Iraq. When the Islamic State took over the facility in early August it raised concerns that the militants had the ability to flood Mosul city in a matter of hours, as well as the capital Baghdad.

An engineer at the dam said the militants had told residents to leave the area, according to Reuters. Anticipating the advance of Kurdish fighters, they had planted roadside bombs around the facility, the engineer added.

American air force planes had targeted positions close to Mosul dam over Saturday and Sunday.

US President Barack Obama said the airstrikes were aimed at protecting American interests in the vicinity.

In a letter to Congress, Obama warned that disruption to the dam could put US staff and facilities at risk, while its failure could also "prevent the Iraqi government from providing critical services to the Iraqi populace."

It is the first instance in which the US has sent bombers on missions over Iraq since the Islamic State captured territory around Mosul.