AL-QOSH, Iraq - Iraqi Kurdish fighters backed by US warplanes retook the country's largest dam from militants on Sunday, as Sunni Arab tribesmen and security forces fought the militants west of Baghdad.

The recapture of Mosul dam marks the biggest major prize clawed back from Islamic State (IS) militants since they launched their offensive in northern Iraq in early June when they swept Iraqi security forces aside. IS militants, who have declared a "caliphate" straddling vast areas of Iraq and Syria, also came under air attack in their Syrian stronghold of Raqa on Sunday, a monitoring group said. Syria's air force carried out 16 raids on the city of Raqa and several more on the town of Tabqa in Raqa province, killing at least 31 jihadists and eight civilians, said the Syrian Observatory for Human Rights. Two months of violence have brought Iraq to the brink of breakup, and world powers relieved by the exit of divisive premier Nuri al-Maliki are sending aid to the hundreds of thousands who have fled their homes as well as arms to the Kurdish peshmerga forces.

Buoyed by the air strikes US President Barack Obama ordered last week, Kurdish forces are fighting to win back ground they had lost since the start of August, when the jihadists went back on the offensive north, east and west of the city of Mosul, capturing the dam on August 7. Earlier Sunday, US warplanes and drones pummelled the militants fighting against the Kurdish advance.

The US Central Command reported that the military had carried out 14 air strikes during the day near the dam, which, located on the Tigris river, provides electricity and irrigation water for farming to much of the region. CENTCOM said the strikes destroyed 10 IS armed vehicles, seven IS Humvees, two armoured personnel carriers and one IS checkpoint.

An AFP journalist saw towers of smoke rising from the area of the dam, apparently from the sites of strikes. In Syria's Raqa, the air strikes were the "most intensive" against the IS since the jihadists joined the anti-regime revolt in that country in spring 2013, the Observatory said. "The regime wants to show the Americans that it is also capable of striking the IS," said the Britain-based group's director, Rami Abdel Rahman. In western Iraq's Anbar province, security forces backed by Sunni Arab tribal militia, who announced a new effort against the jihadists on Friday, made gains west of the provincial capital Ramadi, police said. Fighting was also taking place near the strategic Euphrates Valley town of Haditha, located near another important dam, police Staff Major General Ahmed Sadag said.

The rallying of more than two dozen Sunni tribes to the government side marked a potential turning point in the fightback against the jihadists and their allies. The militants were able to sweep through the Sunni Arab heartland north and west of Baghdad in June, encountering little effective resistance, and Iraqi federal security forces have yet to make significant headway in regaining ground. Anbar was the birthplace of the Sahwa, or Awakening, movement of Sunni tribes that from late 2006 sided with US forces against their co-religionists in Al-Qaeda, helping turn the tide against that insurgency.

In the north, members of minority groups including the Yazidis, Christians, Shabak and Turkmen, remain under threat of kidnapping or death at the hands of the jihadists. On Friday, IS fighters killed around 80 Yazidi Kurds in the village of Kocho near the northwestern town of Sinjar, Kurdish officials said.

The jihadist' storming of Sinjar on August 3 sent tens of thousands of civilians fleeing onto Mount Sinjar, prompting an international aid operation and helping to trigger the launch of US air strikes. The Yazidis' non-Muslim faith is anathema to the Sunni extremists of IS. Human rights groups and residents say IS fighters have been demanding that religious minorities in the Mosul region either convert or leave, unleashing violent reprisals on any who refuse. Amnesty International, which has been documenting mass abductions in the Sinjar area, says IS kidnapped thousands of Yazidis in this month's offensive.

 Tens of thousands have fled, most of them seeking refuge in areas of northern Iraq under Kurdish control, or in neighbouring Syria.