"The analogy we use around here sometimes, and I think is accurate, is if a jayvee team puts on Lakers uniforms that doesn’t make them Kobe Bryant."

US-backed Iraqi forces announced Thursday they have retaken one of Islamic State's remaining strongholds after hundreds of militants surrendered amid fresh signs the terror group is collapsing and unable to defend its territory.

'They're giving up,' said Lieutenant General Paul Funk, who commands the coalition task force fighting Islamic State in Iraq and Syria. 'Their leaders are abandoning them.'

In uncommon scenes, large groups of militants were turning themselves over to Kurdish Peshmerga forces, in the city southwest of Kirkuk.

The fall of Hawija in northern Iraq, after two weeks of fighting, is the latest in a string of defeats for Islamic State, also known as ISIS, and suggests the rank-and-file fighters are demoralised as the group struggles to defend what remains of the territory it seized in 2014.

'The speed at which the enemy gave up surprised me,' Funk said in a phone interview from Baghdad, after Iraqi Prime Minister Haider al-Abadi announced the liberation of Hawija.

Funk said about 1,000 militants surrendered in the past three or four days of fighting in Hawija. The coalition had estimated up to 1,500 militants were defending the city when the offensive began.