The operation was led by the autonomous Kurdish region's peshmerga forces but also involved fighters from the Yazidi minority, which IS targeted in a brutal campaign of massacres, enslavement and rape. It cut a key supply line linking jihadist-held areas in Iraq with those in Syria.

Across the border, the Syrian Democratic Forces coalition said it also delivered a blow to IS logistics, announcing that it had driven the jihadists out of Al-Hol, an important village on their Iraq-Syria supply route.

The gains against IS are the latest sign that the jihadist group, which won a series of victories in a stunningly rapid offensive in Iraq last year, is now on the defensive.

In remarks Friday, US President Barack Obama expressed satisfaction with efforts against IS, saying the group's expansion has been curbed.

"From the start, our goal has been first to contain, and we have contained them," Obama said.

Barzani, the president of Iraqi Kurdistan, told a news conference near the northern town: "I am here to announce the liberation of Sinjar."

His remarks also made clear that political conflict over Sinjar would likely follow the military battle for the town.

"Sinjar was liberated by the blood of the peshmerga and became part of Kurdistan," Barzani said.

Baghdad, which has long opposed Kurdistan's desire to incorporate a swathe of disputed northern territory, is unlikely to welcome that idea.

- Flags, celebratory gunfire -

Earlier in the day, hundreds of Kurdish fighters, dressed in camouflage uniforms and armed with assault rifles and machineguns, moved into the town on foot, an AFP journalist reported.

Carrying the Kurdish region's flag, they fired into the air and shouted "Long live the peshmerga!" and "Long live Kurdistan!"

Inside Sinjar, many houses and shops, a petrol garage and the local government headquarters had been destroyed.

Burned out cars sat in the streets, while barrels apparently containing explosives had been left behind.

The huge task of clearing Sinjar of bombs planted by IS remains, and there is also the possibility of holdout jihadists, who have kept up attacks even after other areas in Iraq were said to have been retaken.

Sinjar has been pounded by US-led air strikes and Kurdish artillery fire targeting IS positions, which sent massive columns of smoke drifting up from the town on Thursday.

The coalition carried out 36 strikes against jihadists in the Sinjar area on Wednesday and Thursday, and 15 more across the border in Al-Hol, which the Syrian Democratic Forces announced on Friday they had taken the day before.

And Syrian forces broke a year-long IS siege of a military air base in the country's north Tuesday with backing from Russian air strikes.

In a rare admission Thursday, the Pentagon said US ground forces advising the Kurds on their offensive were close enough to the front to identify IS targets and call in strikes.

Pentagon spokesman Peter Cook told reporters most of the US-led coalition troops were behind the front lines working with Kurdish commanders.

But "there are some advisers who are on Sinjar mountain, assisting in the selection of air strike targets."

On Thursday, Kurdish forces cut the key highway that links IS-held areas in Iraq and Syria.

"Sinjar sits astride Highway 47, which is a key and critical resupply route" for IS, said Colonel Steve Warren, spokesman for the international operation against IS.

"By seizing Sinjar, we'll be able to cut that line of communication, which we believe will constrict (IS's) ability to resupply themselves, and is a critical first step in the eventual liberation of Mosul," said Warren, referring to the jihadists' main hub in Iraq.

IS overran Sinjar in August last year, forcing thousands of Yazidis to flee to the mountains overlooking the town, where they were trapped by the jihadists.

The United Nations has described the attack on the Yazidis as a possible genocide.

Aiding the Yazidis, whose unique faith IS considers heretical, was one of Washington's main justifications for starting its air campaign against the jihadists last year.