Iraq's Kurdish peshmerga forces on Sunday launched an offensive to retake areas east of Mosul, the Islamic State's main hub in the country, a statement said.
The "peshmerga-led ground offensive, backed by international coalition warplanes" started before dawn, the Kurdistan Region Security Council (KRSC) said.
It said the operation involved around 5,500 peshmerga and was aimed at retaking several villages from the IS near Khazir, east of Mosul.
"This is one of the many shaping operations expected to increase pressure on ISIL (IS) in and around Mosul in preparation for an eventual assault on the city," the KRSC said.
Ten hours into the operation, a KRSC update said three villages had been fully retaken.
It also said that five suicide car bombs were destroyed by peshmerga forces and coalition air strikes.
AFP reporters on the front line saw what appeared to be US-led coalition military advisers working with the peshmerga.
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Some of them told reporters in English that taking pictures and footage of their presence was banned and asked that anything already recorded be deleted from cameras.
It was not clear what their nationality was, although one was seen with a large US flag.
The US-led coalition has thousands of forces deployed across the country on an "advise and assist" mission meant to help Iraqi forces battling IS without directly engaging in combat operations.
Many have been deployed on the northern front with the Kurdish forces leading operations around Mosul, but they usually keep a very low profile.
The US military reported that coalition aircraft had carried out 12 strikes against IS targets near Mosul on Saturday alone, an above average number for a single area on a single day.
The coalition's definition of a strike allows for a number of separate targets to be hit in one strike, and a statement listed a large number of destroyed targets in Saturday's raids.
Besides taking out top IS leaders, degrading the group's infrastructure and preventing attacks, one of the primary roles of coalition air support has been to pave the way for ground operations by Iraqi forces.
The fresh push against the jihadist organisation comes a week after Iraqi forces launched an operation against Fallujah, IS's only other major urban hub in Iraq.