Paratroopers of the US 173rd Airborne brigade on Thursday dug in at a mountain air strip after 1,000 men were dropped overnight to help protect the Kurdish autonomous zone and to launch possible assaults on Iraqi forces towards the south and the west.

In an operation lasting almost eight hours, US aircraft ferried the troops over the drop zone on the rain-sodden plain that surrounds the air strip, 80km north of the Kurdish capital of Arbil. As the parachute drop was under way, US aircraft attacked forward Iraqi positions near Kalak, 37km west of the city.

Several thousand more US soldiers are expected to arrive in the Kurdish zone in the next two to three days, although the force will fall far short of the 40,000-60,000 the Pentagon planned to put into a northern front.

Turkey's refusal to open a land bridge for US troops and equipment has forced military planners to scale back operations in the north and to forge an alliance with the Kurdish authorities and their 60,000-strong regular forces.

Kurdish officials said operations in the north would not follow the same pattern as the coalition offensive in southern Iraq.

"I think there will be more US troops here," said Hoshyar Zebari, a leader and spokesman of the Kurdistan Democratic party (KDP), which controls this part of the Kurdish zone. "But you can't fight on a 500km front from Syria to the Iranian border, manned by nearly 100,000 Iraqi troops, with just a few thousand US special forces and paratroopers."

The Iraqi front line is as close as 7km from Arbil and is manned by at least three divisions of the Iraqi 1st and 5th armies, guarding the way to Kirkuk and Mosul. Mr Zebari said US air cover made it impossible for Iraqi armour to mount an offensive into the Kurdish zone.

The 173rd Airborne's arrival was co-ordinated with the Kurdish forces, who were yesterday mingling with US soldiers at the perimeter of the 1,500-metre strip. Two attack helicopters and three military trucks were parked near the air strip as soldiers dug foxholes in the soft ground and set up machine-gun positions.

"They don't have to worry, we will guard them," said Mahmud Soar, a local teacher, welcoming the arrival of the largest US force so far to reach the north.

The KDP's Mr Zebari said it was likely the paratroopers would be engaged in offensive operations against the Iraqi forces. "This is a fighting force," he said. "It is my understanding that these forces that have been introduced here are for operational use against the Iraqi army."

If the US forces are used for offensive operations, it would probably be to attack specific targets rather than to open a broad front. Among the areas the US would like to secure are the oilfields north of Kirkuk.

Referring to the Kurdish role in military operations, Mr Zebari said Kurdish units were already operating along and behind the Iraqi lines in co-ordination with the US. The Kurds, using their network of contacts in Mosul and Kirkuk, have been seeking to persuade Iraqi regular army commanders not to resist coalition forces.

"If we launch an attack," said Mr Zebari, "it will be at the time and place of our choosing, but it will not be behind the backs of the Americans."

He said he believed the difficulties the allies were encountering in the south would prompt a reappraisal of military strategy and oblige US-led forces to place greater emphasis on using the Iraqi opposition.

"The paramilitary and security forces in the towns are better known to us than they are to the coalition and we are better placed to take care of them," said Mr Zebari. He said that elements of Saddam Hussein's Ba'ath party who resisted "will be overcome".

The Kurdish forces were equipped mainly with light weapons and, although there was currently no shortage of these, the US had yet to provide heavier equipment.

"We are not in a rush," said Mr Zebari. "As long as we are safe and protected and taking care of our areas, we are comfortable.

"We can help, but we are not desperate. We want to see the coalition win this war as quickly as possible but that doesn't mean we want to see it dragged into a quagmire."