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

The clashes kicked off at 9:00 am (0600 GMT) around 30 kilometersmiles) east of Mosul, with exchanges of automatic fire between the Iraqis and Kurdish and US forces that had crept up on Khazer, where the Iraqis maintain a military base.

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.

The bombardment started at about 11:30 am (0830 GMT) and lasted one hour, a US sergeant said, speaking on condition of anonymity.

Later the Iraqis launched a counter-attack, sending a few men to attack Kurdish positions and forcing the US troops to take cover in a bunker. US air support was again called in at around 5:00 pm (1400 GMT), with at least seven strikes launched.

Later Thursday, Kurds were sending reinforcements towards Khazer, and Iraqi mortar fire was continuing.

Khazer and its Manquba bridge are strategic points in the advance on Mosul, 400 kilometers (250 miles) north of Baghdad.

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.

There was no immediate information on casualties.

A US sergeant said some 200 to 250 Iraqis were fighting around Khazer against 120 Kurds. Seven members of US special forces were also present, notably radioing coordinates for the air strikes.

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, security officer Bikas Bekhudan told AFP. Two of the injured were women.

Late Wednesday, Iraqi troops relinquished military positions on a hill overlooking Kalak, which is located some 40 kilometers (25 miles) from Mosul, on the demarcation line between Kurdish- and government-controlled territories.

One US officer said they had pulled back to Mosul, leaving some men at Khazer.

At around 5:00 am (0200 GMT) 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, Kurdish commander Serbat Babili said.

In another development, Kurdish military sources said US and Kurdish forces had stepped up joint operations including on the edge of Kirkuk, harassing Iraqi forces and calling in targeted airstrikes.

The Patriotic Union of Kurdistan (PUK), one of the two factions controlling northern Iraq, said Thursday that its forces would not move against Kirkuk.

"The PUK will not move against Kirkuk as Kurds. Should a decision be taken to move it will be done as the Iraqi opposition and in tandem with the coalition," said Barham Salih, the PUK's prime minister.

Turkey, which has built up forces on its border with northern Iraq, is closely watching Kirkuk which the Kurds have in the past eyed as their future capital. Ankara fears moves towards Kurdish independence during the war could be a green light for renewed unrest among its own large Kurdish minority.

In Arbil, Kurdish fighters claimed on Thursday to have captured 40 Iraqi soldiers in northern Iraq and said more than 60 other soldiers and pro-government armed tribesmen had defected to their ranks.

The report could not be independently confirmed, but a military official said the men were captured in Bashiqa, kilometers (13 miles) northeast of Mosul.

SPACE.WIRE