BANNU, Pakistan (AP) -- Pakistani jets pounded targets in the country's northwest on Monday as the military waged an offensive against militant safe havens that killed 37 fighters, while insurgents fought back with a roadside bomb that killed six soldiers, the first army casualties of the operation, the military said.
The airstrikes are part of a long-awaited operation against foreign and local militants in North Waziristan, an essentially lawless tribal region which has served as a training base for militants and a staging point for insurgents who attack Pakistan and NATO and Afghan troops across the border. The operation started Sunday.
The United States has for years complained to Pakistan about its failure to impose order in a region harboring what Washington considers the country's most dangerous militants, and has carried out hundreds of drone strikes in the area.
The offensive marks the end of the government's policy of trying to negotiate with Pakistani Taliban militants instead of using force to end years of fighting which has killed tens of thousands of civilians and security forces.
Prime Minister Nawaz Sharif, who has promoted the talks, defended military action during a speech to parliament on Monday. Sharif said the government had tried for more than four months to talk to the militants but their violence continued. He said Pakistan could not become a safe haven for militants.
The airstrikes early Monday targeted six hideouts in the Shawal area near the border with South Waziristan, a neighboring tribal region, killing 27 militants, the military said.
Separately, the military said seven militants were killed trying to escape Mir Ali, one of the two main towns in North Waziristan, and another three were killed by snipers while trying to lay roadside bombs near Miran Shah, the region's other main town. Three Pakistani troops were wounded in an exchange of fire with militants.
The military said in a statement that six troops died and three were wounded by the roadside bomb as the Pakistani Taliban warned that more violence could be in the offing.
A spokesman for the militants warned in a statement sent to reporters that international investors, foreign airlines and multinational organizations should leave Pakistan or they'd be considered supporters of the government and fair game.
Shahidullah Shahid also vowed to retaliate in the cities of Islamabad and Lahore, saying they would burn the mansions of the country's rulers. Those cities have largely been spared the bombings and shootings that plague places like Karachi and Peshawar.
Security was being stepped up across Pakistan. In Karachi, a city vital to the country's economy, armored personnel carriers could be seen rolling out the gates of a military base. The military said they were being used to protect sensitive installations.
Few details have been released about the size of the operation or the military assets involved.
The military said troops were sealing off the North Waziristan borders and the main cities, ensuring the evacuation of civilians in addition to establishing areas where militants can surrender their weapons. The military said the campaign was progressing as planned and that no operations had been launched in civilian areas so far.
Residents reached by telephone reported hearing loud explosions overnight but said they cannot go outside because there is a curfew in place.
"We have been just hearing big bangs and explosions. We can't go out to see what's happening out there," Sajid Dawar, a resident of Miran Shah, said by telephone. He urged authorities to help people leave as quickly as possible.
Another resident, Ziaullah Khan from Mir Ali, said people were starting to run out of food because the markets had been closed for a few days.
North Waziristan is one of the last parts of the tribal regions where the military has not launched a large operation. Militant groups including the Pakistani Taliban, al-Qaida and the Haqqani network have long used the region as a base.
The Pakistani military said it has asked the Afghan government for help reinforcing its side of the border, to prevent militants from fleeing.
Afghanistan and Pakistan have argued repeatedly over violence along the porous border, accusing each other of failing to act against insurgents.
Kabul accuses Pakistan of failing to take action against militants such as the Haqqani network, who are believed to be responsible for some high-profile attacks in Afghanistan.
Critics also say Pakistan maintains a so-called "good Taliban, bad Taliban" policy in which it combats the Pakistani Taliban, who attack the state, but tolerates or supports the Afghan Taliban in order to maintain influence in the neighboring country.
The offensive comes a week after militants laid siege to Pakistan's largest airport in an attack that shocked the country and appeared to mark a turning point in the government's thinking about military action.
But the large military operation could spark
a wave of bloody reprisal attacks, especially in Karachi or Peshawar, where militants already have a sizeable presence.
Even before the airstrikes, residents in North Waziristan were leaving the area due to previous airstrikes and fear of a larger operation. So far 50,000 people have left, provincial Gov. Sardar Mehtab Ahmed Khan said.
Nawal Khan Dawar from Mir Ali said he arrived in Bannu six days ago with his family after an airstrike nearby destroyed several houses. He said he rented a house for his family but, without any work, he doesn't know how long they'll be able to stay. He's worried about other family members still in North Waziristan.
"We don't know what is happening with them. We have not heard from them," he said.
Some of the displaced were even going to Afghanistan. Mubariz Mohammad Zadran, a spokesman for the provincial governor of Afghanistan's Khost province, said over the last two weeks more than 400 families have entered from North Waziristan.
Santana reported from Islamabad. Asif Shahzad and Zarar Khan contributed from Islamabad, Adil Jawad in Karachi and Rahim Faiez from Kabul.