Pakistani fighter jets resumed air strikes in North Waziristan on Monday, a day after the army announced the start of a full-scale military operation to flush 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, Pakistan 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.
Military sources said combat aircraft pounded targets in the Shawal sector of North Waziristan, home to some of Pakistan's most feared militants and al Qaeda commanders, early on Monday.
"Around 15 militants, mostly Uzbeks, have been killed in Monday morning air strikes in Shawal area of North Waziristan," a security source told Reuters in the regional capital, Miranshah.
"Fighter jets targeted three militant hideouts in the area," he said. Another official put the death toll at 21.
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.
Sharif, who has not commented publicly on the operation yet, was due to address parliament later on Monday.
The United States, in the process of withdrawing troops from neighbouring Afghanistan, also wants Pakistan to do more to crush the insurgency and eliminate al Qaeda hideouts tucked away in the remote mountains straddling the frontier.
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, leading to food shortages in some places.
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 Afghanistan, where they have relatives.
"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 empty.
The curfew will be relaxed in the next couple of 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.
The all-night attack on Karachi airport by a band of highly trained Uzbek fighters 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.
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.
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 all but deserted as the operation got underway on Sunday afternoon.
The Pakistani Taliban are allied with Afghan insurgents of the same name but operate as a separate entity, uniting dozens of smaller jihadist groups based in the tribal areas.