As a result of this unusual combination of factors, there has been little of the sectarian violence in the Kurdish-controlled city that has engulfed vast swathes of Iraq since the bombing of a Shiite shrine in February last year.

Instead, Arbil boasts of a flourishing economy and has become a major destination for hundreds of thousands of people fleeing the violence in other parts of Iraq.

An attack on February 1, 2004 which killed 105 people "turned the population against the terrorists," said local official Sabah Karim in the Arbil office of Asayish, the Kurdish security forces.

"Since then, there has been total cooperation. If somebody sees an unknown person taking photographs, any unusual movement or anything out of the ordinary, they call us."

The walls of his office, riddled with pockmarks, seem to contradict his statements -- these are the scars of an attack on September 5 this year in which 14 people were killed when a truck bomb exploded under its windows.

"It was the first in three years -- a Saudi suicide bomber with two Kurdish accomplices ... Not people from here ... We can't prevent everything," Karim said with a shrug.

Faced with an influx from other provinces, the Kurdish regional authorities have instituted a "residence permit" against the advice of Iraq's central government.

"It is a means to check who is this person, where he comes from, who is his family," said Karim.

Newcomers are obliged to have a Kurdish guarantor. "If there is any suspicion, the guarantor must bring us the stranger. If not, he will be arrested."

A European observer who has been based in Arbil for almost four years, said the residence permits are strictly controlled.

"(It) is given for one month, three months ... Each renewal is a fresh control," said the observer, speaking on condition of anonymity.

"There is an office of the Kurdistan Democratic Party (the party of regional president Massud Barzani) in each neighbourhood. The first step is information: who is this person. Why is he returning home so late? Who are these strangers? It is very effective."

To prevent what Sabah Karim described as the "Arabisation" of the Kurdish region, non-Kurds are forbidden to buy houses or apartments.

If an apartment is rented out, the owner is strongly advised to keep a close eye on the tenant.

"Our real strength," Karim says with a smile, "is information. We are very informed on what happens. And we keep a close eye on the few Arab villages in the region."

At the end of 2003, at the instigation of the US military, an excavator was used to dig a ditch right around Arbil -- four metres (13 feet) wide and three (10 feet) deep, impassable by vehicle, difficult on foot.

The effect of the ditch is to restrict traffic access to the city to just eight entrances, which are strictly supervised.

Captain Shamal -- he refused to give his full name -- is in charge of one of the eight points, three kilometres (two miles) from the city on the road to Dohuk.

"Most important is the accent," he says. "Within two words we know if this is somebody from Arbil or not. We question those we don't know. We know all the truck drivers. We can quickly pick out a new face."

Peshmerga fighters are deployed along the entire length of the ditch every 500 metres (550 yards), in sight of one another, equipped with binoculars and night vision equipment.

"No-one passes by without us knowing -- even on foot," the captain says. "The guys do a good job. Gangsters and terrorists hesitate before entering my city."