* Army says kills 27 militants in air strikes
* Troops cordon off region, curfew imposed
* Six Pakistan troops killed by roadside bomb
* About 10,000 refugees flee to Afghanistan
* Karachi airport up and running after attack (Adds army statement)
By Haji Mujtaba
MIRANSHAH, Pakistan, June 16 (Reuters) - Pakistani fighter jets pounded North Waziristan on Monday, a day after the army announced the start of a full-scale drive to flush Islamist insurgents out of the volatile region bordering Afghanistan.
In a long-awaited military operation precipitated by a deadly insurgent attack on Pakistan's biggest airport a week ago, Islamabad has deployed troops, artillery and helicopter gunships to fight insurgents in North Waziristan.
The Taliban and their ethnic Uzbek allies holed up in North Waziristan have both claimed responsibility for the June 8 commando-style attack on Karachi airport, which was seen as a strategic turning point in how Pakistan tackles the insurgency.
In a chilling message issued in response to the offensive, the Taliban said foreign firms operating in Pakistan would bear the brunt of their revenge.
"We are in a state of war. Foreign businesses, airline companies and multinationals should immediately sever their ties with Pakistan or they will have only themselves to blame for any damage," said Pakistani Taliban spokesman Shahidullah Shahid.
The army said combat aircraft destroyed six hideouts in the Shawal sector of North Waziristan, home to some of Pakistan's most feared militants and al Qaeda commanders, early on Monday.
"In these precise strikes, 27 terrorists were killed. There is no (civilian) population in the area," it said.
"North Waziristan Agency has been isolated by deploying troops along its border with neighbouring agencies and FATA (Federally Administrative Tribal Areas) regions to block any move of terrorists in and out of the Agency."
The army chief, Raheel Sharif, said the operation would continue until "all terrorists along with their sactuaries" were eliminated but gave no specific timeline.
"The operation is not targeted against our valiant tribes of North Waziristan but against those terrorists who are holed up in the agency and have picked up arms against the state of Pakistan," an army statement on Monday quoted him as saying.
The army said troops had cordoned off militant bases, including the town of Mirali where ethnic Uzbek and other foreign fighters are based, and the regional city of Miranshah.
The Taliban appear determined to fight back. In the first attack since the start of the operation, at least six Pakistani soldiers were killed on Monday when a roadside bomb hit an army convoy just north of Miranshah, the army said.
The all-night attack on Karachi airport all but destroyed prospects for peace talks with the Taliban militants, who are fighting to topple the government and impose a strict Sharia-based theocracy in the nuclear-armed nation.
The airport has since resumed operations after suspending flights twice in the aftermath of the attack.
Public opinion appears to have swung in favour of a military operation after the Karachi attack, even though such a response in North Waziristan means a higher risk of revenge attacks by the Taliban outside the tribal region.
"Operation at last!" The Nation daily said in a front-page headline.
Prime Minister Nawaz Sharif has long insisted that he could bring insurgents to the negotiating table but the start of the offensive is seen as a victory for hawks in the army who have long called for tough military action.
"We know the difficulties of picking this option (of launching an operation), but the enemy has left us no choice," Sharif told parliament in his first remarks on the operation.
"The world knows that on the one hand we were engaged in dialogue with these people, and on the other hand our children, women and youth were being bathed in blood."
He added: "It is a matter of sorrow and pain that after four and a half months of talks, we could not make a breakthrough for peace."
OPERATION "PROPHET'S SWORD"
The army imposed an all-day curfew in North Waziristan as the operation got under way and turned off mobile phone services to undermine the insurgency and restrict people's movements.
Independent confirmation of the events or other details were not available immediately from a region where journalists are not allowed to operate freely.
Expecting an escalation of violence, two-thirds of families have fled from the ethnic Pashtun region, residents said, many heading for the Gorbaz district of Afghanistan's Khost province.
Mohammad Akbar Zadran, Gorbaz district chief, told Reuters nearly a thousand families, or around 10,000 people, had now entered Gorbaz district, and the number was growing.
"We have packed up everything and are ready to leave as soon as the curfew is lifted," said Ethasham Khan, a resident of Miranshah, where the usually bustling streets were empty.
The curfew would be relaxed in the next few days to allow residents to leave the area, a security official said.
Tellingly, the Pakistani military's operation against the Islamist militants in North Waziristan is called Zarb-e-Azb in Urdu, or "Strike of the Prophet's Sword".
For now, ground troops - numbering some 80,000 in North Waziristan, according to military sources - have not been involved in direct military action, leaving F-16 combat jets to lead the offensive with air strikes.
It was also unclear how long officials expect the operation to last in a region of forbidding mountainous terrain that has never been subdued by any government.
Separately on Monday, Omar Jillani, an intelligence official who police said is the nephew of Pakistan's powerful chief justice, was kidnapped in the eastern city of Multan by suspected Taliban gunmen, police said.
Security is visibly tighter in the capital, Islamabad, as well, with street patrols by paramilitary Rangers and police. In Lahore, the cultural capital, police have added checkpoints.
Islamabad's central Kohsar market, a shopping and dining spot for foreigners and rich Pakistanis, was largely deserted as the operation got under way on Sunday afternoon. (Additional reporting by Asim Tanveer in Multan, Elyas Wahdat in Khost, Hamid Shalizi in Kabul, Mehreen Zahra-Malik in Islamabad; Writing by Maria Golovnina; Editing by Tom Heneghan)