Forces loyal to Saddam Hussein started firing artillery and then rockets at about 10:30 am (0630 GMT) on positions they abandoned the day before near the line marking the border between Kurdish-controlled territories and the rest of Iraq they have progressively abandoned since Wednesday.

They have at least partially regrouped near Khazer, about a dozen kilometres (eight miles) from the positions east of Mosul, a majority-Arab city of 1.5 million in a mostly Kurdish area located 400 kilometersmiles) north of Baghdad.

Khazer and its Manquba bridge are strategic points in the advance on Mosul.

One of its roads leads to Mosul, and the other to Bardarash in the northeast, to which Iraqi forces pulled back on Wednesday after battling Kurdish and US forces.

Coalition-backed Kurdish fighters clashed Thursday morning with Iraqi troops near Khazer, as US special forces and Kurds advanced on the oil capital of Kirkuk.

The intense fighting prompted Kurdish special forces chief Waji Barzani to say the "northern front has opened."

When the Iraqis began firing 60 and 120 millimeter cannons at them, US and British planes were called in to bomb their positions, Kurdish sources said.

Kurdish fighters told AFP the bombing continued until about midnight, and started again around dawn.

The said the Iraqi side responded with mortar shells late Thursday which hit Kalak, located on the demarcation line some 40 kilometers (25 miles) east of Mosul.

There was no immediate word on casualties.

On Thursday, some 40 peshmerga (Kurdish fighters) and four US special forces took up positions on the hill near Kalak, and then sent some men to the edge of Khazer, about two kilometers (1.2 miles) from the Iraqi soldiers, according to the Kurds.

Iraqi forces also fired several mortar rounds at the Kurdish town of Khabat, 10 kilometers (six miles) from Khazer, killing one civilian and injuring three others, one seriously, they said.

Despite the strong pressure, "the Iraqis are still dug in at Khazer and still hold Manquba bridge," one of the peshmerga said.

He added that his comrades were positioned some 500 metres (yards) from the bridge.

Kurdish reinforcements headed by truck toward Khazer Friday morning, although there were no further details on their destination.

The peshmerga also lifted their roadblock preventing journalists from entering the area.

SPACE.WIRE