Iraqi forces advancing on Mosul have faced stiff resistance from Islamic State militants, despite an unprecedented wave of US-led coalition air strikes in support of the week-old offensive.

Federal forces and Kurdish fighters gained ground in several areas, but the jihadists have hit back with shelling, sniper fire, suicide car bombs and booby traps.

ISIL has also attacked Iraqi forces elsewhere, the latest coming on Sunday near the Jordanian border.

Following a weekend visit to Iraq by US Defense Secretary Ashton Carter, American officials said the coalition has destroyed 136 ISIL fighting positions, 18 tunnels and 26 car bombs.