At least 31 people were killed in the offensive, which sent some residents of Lower Dir district fleeing carrying small children and few belongings.
The operation appeared to endanger a peace pact struck with Taliban militants in neighboring Swat Valley, although a top official insisted the deal was "intact." Another official demanded the insurgents disarm, but a Taliban spokesman said the militants would not give up their weapons.
The Lower Dir offensive also came ahead of Pakistani President Asif Ali Zardari's scheduled meeting with President Barack Obama in early May, but Pakistani officials denied outside pressure influenced the move.
Television footage from the district showed at least two helicopter gunships heading toward the mountains. Troops guarded a road blocked with paramilitary trucks, while some families sat nearby. Another family headed away in a vehicle packed with luggage. The operation killed at least 30 militants, including a commander, plus one paramilitary soldier, according to an army statement and Interior Ministry chief Rehman Malik. The statement said the operation was launched at the request of the provincial government and local residents, but did not detail its scope or expected duration.
The government agreed to impose Islamic law in Swat and surrounding districts that make up Malakand Division if the Taliban there would end their violent campaign in the one-time tourist haven. Critics labeled the deal a "surrender" to the militants and warned Swat could turn into a haven for allies of Al-Qaeda. In recent days, Taliban forces from Swat began entering Buner, a neighboring district which lies just 60 miles (100 kilometers) from the Pakistani capital, Islamabad. Officials said most of the insurgents pulled out of Buner on Friday amid reports of possible military action, and threats that the government would scrap the deal.
Losing either Lower or Upper Dir to militants would be a blow not only for Pakistan but also for the US because a part of the region borders Afghanistan, where the US is sending thousands more troops to shore up the faltering war effort against a resurgent Taliban. Farhatullah Babar, spokesman for Pakistani President Asif Ali Zardari, insisted the offensive did not render the peace agreement moot.
He said the government would fulfill its pledge to establish an Islamic judicial system in Malakand, a long-standing demand of local residents exhausted by the inefficient regular courts - and a grievance exploited by the Taliban.
"The peace deal is intact," Babar said. "At the same time the government is determined to root out the militants hell-bent on destroying the law and order situation."
But Malik, the head of the Interior Ministry, even spoke of the deal in past tense when saying the Swat militants had to disarm. "Enough is enough," Malik said. "There is no option for them except to lay down their arms, because the government is serious now to flush them out."
Taliban spokesman Muslim Khan said the militants, "do not lay down weapons. Instead they snatch them." He said the Taliban were still trying to abide by the deal but wanted to make sure the newly created Islamic courts had full authority.
Amir Izzat, a spokesman for the hard-line cleric who mediated the deal, said the "operation is a clear violation" of the agreement and warned that the government would be responsible for the fallout. A similar peace deal attempted in Swat last year fell apart within a few months, and officials said it gave the militants there a chance to regroup and rearm, making them a more challenging enemy when the army resumed its fight in the valley.
Mahmood Shah, a former security chief for Pakistan's tribal regions, said the army operation in Dir was a clear signal to the Swat Taliban that they must stop entering neighboring districts. He predicted it would be a "limited" operation.
"The government is sincere in the deal, but the militants don't seem to be," he said. "The government wants them to lay down their weapons, and when they don't, a message goes to everywhere that they have some other agenda instead having an interest in peace. If the government goes for an operation in Swat, this time it will be much stronger and bigger as compared to previous one." Pakistan's attempts to battle militants using military offensives have also had mixed results.
In Bajur tribal region, for instance, officials said earlier this year they'd vanquished the Taliban after a monthslong operation, but recent reports indicate the militants there are regrouping. The Pakistani military's ability or willingness to take on the Taliban has been questioned by some top US officials in recent days, even as they ponder giving Pakistan billions more in military and other aid.
Gen David Petraeus, the head of US Central Command, said Pakistan's leaders should focus on the looming threat posed by extremists within their borders, instead of their rivalry with India.
"The most important, most pressing threat to the very existence of their country is the threat posed by the internal extremists and groups such as the Taliban and the syndicated extremists," Petraeus told a congressional panel.
Babar said the offensive on Sunday had nothing to do with American pressure. "There is no question of pressure by anybody," Babar said.
Some two years worth of clashes between the military and insurgents in Swat killed hundreds of people and displaced up to a third of the valley's 1.5 million people.