The advances came as Pentagon sources claimed that several of the Islamic State group's key leaders were killed in US strikes in recent weeks, including the top commander for Iraq.

The two-day blitz into the Sinjar region involved 8,000 peshmerga fighters and some of the heaviest air strikes since a US-led coalition started an air campaign four months ago.

Masrour Barzani, who is the son of the Kurdish president and the intelligence chief for the autonomous region, said the peshmerga advance had broken the siege on Mount Sinjar.

"Peshmerga forces have reached Mount Sinjar, the siege on the mountain has been lifted," he told reporters from an operations centre near the border with Syria.

The peshmerga said they recaptured eight villages on the way and killed about 80 IS fighters in the initial phase of the offensive launched from Rabia on the Syria border and Zumar on the shores of Mosul dam lake.

They also lost seven men on Wednesday in Qasreej village when they failed to stop a suicide attacker who rammed an explosives-laden armoured vehicle into their convoy, officers told AFP on the scene.

"This operation represents the single biggest military offensive against IS and the most successful," a statement from Barzani's office said.

A devastating IS attack on the Yazidi minority's Sinjar heartland in August displaced tens of thousands of people and was one of the reasons put forward by US President Barack Obama for launching a campaign of air strikes in September.

Amid fears of a genocide against the small Kurdish-speaking minority, tens of thousands of Yazidis fled to the mountain and remained trapped there in the searing summer heat with no supplies.

Kurdish fighters, mostly Syrian, broke that first siege but remaining anti-IS forces were subsequently unable to hold positions in the plains and retreated back to the mountain in late September.

- Baghdadi deputy -

The peshmerga commander for the area said troops had reached the mountain and secured a road that would enable people to leave, effectively breaking the siege. Several thousand are still thought to be trapped there.

"Tomorrow most of the people will come down from the mountain," Mohamed Kojar told AFP by phone, explaining the offensive had secured a corridor northeast of the mountain.

A Yazidi leader atop the mountain however said he could see no sign of a military deployment. A peshmerga commander explained that any evacuation would only begin on Friday.

Kurdish officials said the operation had dealt the jihadists a blow by cutting their supply lines and forcing them retreat tourban bastions such as Tall Afar and Mosul, their main hub.

Jihadists still control of the town of Sinjar, on the southern side of the mountain and many of the surrounding villages.

The peshmerga have said that the aim of the operation launched on Wednesday was to liberate the entire Sinjar area.

In Washington, a US defence official announced that three top IS leaders in Iraq had been killed in US air strikes in recent weeks.

Among them was Fadel Ahmed Abdullah al-Hiyali, a deputy of IS supremo Abu Bakr al-Baghdadi in charge of operations in Iraq and best known as Abu Muslim al-Turkmani.

"We've long said that command and control, including leadership, remain valid targets," the US defence official told AFP on condition of anonymity.

There was no hint that Turkmani had been killed on the jihadist social media accounts and forums that usually relay such information.

The jihadist group proclaimed a "caliphate" over parts of Iraq and Syria nearly six months ago after sweeping through Iraq's Sunni heartland and throwing the country into chaos.

A second wave of attacks in August against Sinjar and towards the borders of Kurdistan triggered a US intervention that has now grown into a 60-nation anti-IS coalition.

The strikes were extended into Syria on September 23.

The military fightback appears to have gradually turned the tide on the jihadists, who have suffered a string of setbacks in Iraq in recent weeks.

Battle lines are more static in Syria, where the West is not coordinating its air campaign with the regime.

"I think they're having a hard time in terms of communicating right now, in terms of resupply," Lieutenant General James Terry, the US commander supervising the anti-IS war, said Thursday.

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