Thousands of Iraqi Kurdish Peshmerga fighters, supported by US special forces, have overrun the main strongholds of an extremist Muslim group accused of having links with terrorism and the al-Qaeda network.
The fighting took place in harsh terrain
After an operation which began at dawn, Peshmerga forces said they had captured all the main centres held by the Ansar al-Islam, who had controlled a string of around 40 villages and small towns in the mountainous north-east of Iraq.
Perhaps as many as 10,000 Kurdish Peshmerga guerrillas took part in this operation.
It began at dawn with an offensive on three fronts up into the mountain towns and villages held by the Ansar.
Within 12 hours the Ansar's main centre at Biara was overrun; its streets were thronged with hundreds of jubilant Peshmergas.
A handful of US special forces were also discreetly on hand.
They had played a vital supporting role, providing some artillery cover and calling in air strikes from American jets which were constantly circling in the sky.
As darkness fell, a senior official of the Patriotic Union of Kurdistan (PUK), the Kurdish faction which carried out the bulk of the attack, said that all the Ansar's main centres had been taken and about 70 of their fighters killed.
The remnants, he said, had taken to the rugged mountains which surround the area and he was confident the entire pocket would be cleared within 24 hours.
Article of faith
As darkness fell, thousands of Peshmerga seemed to be heading home, while others went deeper into the snow-capped mountains in search of the Ansar, who were said to be heading up towards the Iranian border.
Civilians have been fleeing the fighting
Clearing them out of the rugged ravines and crags will be no easy task, and even then there will be the fear that some may take to underground activity such as carrying out car bomb attacks, which have plagued the area for several years.
That is one reason why the PUK was eager to carry out this operation, while for the Americans it was an article of faith, since combating terrorism was one of the reasons they cited for intervening in Iraq.
Neither party wanted the Ansar free to operate behind their backs as they turn their attention southwards to the Iraqi government lines.