Kurdish forces launched an offensive against the Islamic State (IS) jihadist group on Wednesday, cutting a road linking two of the main areas it holds in north Iraq, officials said.

The Kurdistan Regional Security Council said peshmerga forces began a "large-scale offensive" around 7:00 am (0400 GMT).

The drive succeeded in cutting the road between IS's stronghold Mosul, the first city the jihadists took in a June offensive, and Tal Afar, a large town to its west that the group has held for months, senior Kurdish security officials said.

A US-led anti-IS coalition announced it carried out six air strikes in the two areas from Tuesday to Wednesday -- three near Tal Afar and three near Mosul. It did not specify the exact locations targeted.

The strikes hit targets including vehicles, IS units, buildings, heavy weapons and a bridge, a statement said.

IS spearheaded a sweeping offensive that has overrun much of Iraq's Sunni Arab heartland since June, presenting both an opportunity for territorial expansion and a threat to the country's three-province autonomous Kurdish region.

Several Iraqi divisions collapsed in the early days of the offensive, clearing the way for the Kurds to take control of a swathe of disputed northern territory that they have long wanted to incorporate into their region over Baghdad's objections.

But after driving south towards Baghdad, IS then turned its attention to the Kurds, pushing them back toward their regional capital Arbil in a move that helped spark US strikes against the jihadists.

Backed by the strikes as well as international advisers and trainers, Kurdish forces have clawed back significant ground from IS.

The conflict seems set to redraw the internal boundaries of Iraq in favour of broader Kurdish control in the north.