The Pakistani Taliban on Monday warned foreign firms to leave the country and vowed to hit back against the government after tanks, troops and jets were deployed in a long-awaited offensive on their stronghold.
Pakistan's major cities braced for revenge attacks by tightening  security at key installations and ordering soldiers to patrol the streets, while hospitals in the northwest prepared for casualties. 
The offensive in North Waziristan, the main bastion of Taliban and Al-Qaeda militants, was launched a week after a brazen insurgent attack on the country's main airport in Karachi left dozens dead and marked the end of a troubled peace process.
Pakistan's allies, particular the United States, have called for an operation in the mountainous tribal territory to flush out groups like the Haqqani network, which use the area to target NATO troops in neighbouring Afghanistan.
- 'We will burn your palaces' -
But authorities had held back from a final push -- possibly fearful of angering warlords who attack only Afghanistan and of opening too many fronts in their decade-long battle against homegrown Islamist insurgents.
The Tehreek-e-Taliban Pakistan (TTP) warned foreign countries to stop doing business with the government and supporting its "apostate army". 
"We warn all foreign investors, airlines and multinational corporations that they should immediately suspend their ongoing matters with Pakistan and prepare to leave Pakistan, otherwise they will be responsible for their own loss," main TTP spokesman Shahidullah Shahid said in a statement.
"We hold Nawaz Sharif's government and the Punjabi establishment responsible for the loss of tribal Muslims' life and property as a result of this operation," he added, vowing to "burn your palaces" in Islamabad and Lahore.
Large numbers of troops were seen patrolling the streets of Islamabad, Lahore and Karachi.
- Tanks rolling in -
In the northwestern Khyber-Pakhtunkhwa province which borders the tribal zone, the government has declared a state of emergency in all hospitals and told them to prepare for  casualties, said provincial health minister Shahram Khan Tarakai.
Air force jets have been pounding suspected militant hideouts in the region since Sunday and have been joined by tanks and infantry engaging in heavy artillery strikes.
The military on Monday sustained its first casualties, losing six soldiers to a bomb blast at the village of Ghulam Khan, according to an official statement. Three others were injured.
An AFP reporter in North Waziristan's main town of Miranshah said tanks were now stationed in the bazaar. Troops were firing intermittently in the air to warn people not to leave their homes but so far there had been no reports of close combat.
A convoy of Pakistani civilians flee Miranshah to escape from military operations against Taliban militants in the mountainous North Waziristan district on June 14, 2014 
More than 2,000 soldiers could be seen at new posts set up in the mountains. Pakistan already had troops stationed in the tribal district, but these were reinforced in the days leading up to the offensive.
The militants' death toll so far stands at 177, according to the military. The figures cannot be verified independently. 
In the town of Bannu 10 kilometres (6 miles) from the border with North Waziristan, hundreds of military trucks with roof-mounted machine guns were on their way to the combat zone, as were oil tankers and a military field hospital.
At the Kashoo Bridge area, some 25 kilometres northeast of Bannu, tractors were busy levelling the ground to set up a camp for internally displaced people.
Some 62,000 people have fled the region so far for other parts of Pakistan according to official data, with "hundreds of thousands" eventually expected, said Arshad Khan, a relief official.
The military operation, labelled 'Zarb-e-Azb' after a sword the Prophet Muhammad used in battle, is the latest carried out by the military against insurgents since Pakistan joined the US-led "war on terror" after 9/11.
But doubts remain about how sustainable any gains can be and whether Pakistan will abandon its longstanding policy of using jihadist proxies to influence neighbouring countries.
Observers say the strategy has backfired by leading to the creation of insurgents bent on overthrowing the government in Islamabad.
Analyst Ayesha Siddiqa said the offensive appeared to target only those militant groups who were causing trouble for Pakistan, rather than insurgents as a whole.
"You have Uzbeks sitting in Sindh and Punjab as well. Is the idea to hit them all? It's not against all terrorists, it's against a particular kind of terrorist," she said.
Last week's airport siege was claimed by Uzbek militants fighting for the TTP. The attack slammed the door on a peace process that yielded a brief ceasefire from March to April.
The exodus of thousands of fighters across the porous border ahead of the operation meanwhile could mean they will eventually return, as has been the case in past offensives.