The government launched the operation after attacks on supply convoys for the US-led force in Afghanistan and reports of fighters threatening the city of Peshawar.
There has been growing concern about threats to Peshawar since a Taliban force from Khyber entered the city two weeks ago and seized 16 Christians, before later releasing them.
Around 1,500 troops and police commandos were deployed along the Peshawar border with the Khyber tribal region and its suburbs to protect the city's more than 1m populace.
Muhammad Siddiq Khan, a local official, said that a tribal force that had been forced to abandon its posts in the region several months ago returned to the checkpoints on Sunday, he said.
In a nearby village on Sunday, soldiers blew up a building belonging to the Ansar-ul-Islam group, which is purportedly linked to the Taliban and has been accused of sending fighters across the border into Afghanistan.
"There was no resistance as the building used by Ansar-ul-Islam as their centre was empty," a security official said.
The previous day troops had demolished the house and headquarters of Mangal Bagh, head of the separate Lashkar-e-Islam (LI) group, which officials have said is not linked to the Taliban.
Bagh's group has been accused of robbing vehicles on the Khyber Pass, although officials said his men were not responsible for cross-border attacks on the US-led forces in Afghanistan.
Bagh told a newspaper that he did not know why he was being targeted and said his men had never attacked security forces.
"I have told LI volunteers to go home and not to resist any action," he was quoted as saying by The News, an English language newspaper.
Peace talks halted
Baitullah Mehsud, a senior pro-Taliban leader in Pakistan, has reportedly called off peace talks with the government following the start of the offensive.
"The talks will remain suspended until the government stops talking about operations and attacks against us," the Reuters news agency quoted Mehsud as saying.
|About 1,500 troops and police were deployed on the Peshawar-Khyber border [AFP]
A large military contingent was also reported to have reached the Jandula area in South Waziristan.
Another armed group said that an offensive in the area would only create further problems.
"If the government thinks there is any issue to address, that should be resolved through talks not by the use of force," Munsif Khan, spokesman for the Virtue and Voice organisation, said.
"We are ready for talks with the government."
Yousuf Raza Gilani, Pakistan's prime minister, denied that the government had launched the offensive after pressure from Washington and said negotiations with armed groups in the northwest would continue.
"This is our war and it is for our own survival," hei told reporters after a meeting of former premier Benazir Bhutto's Pakistan People's Party in Lahore.
"Nobody will be allowed to execute others publicly, kidnap minorities, set fire to girls' schools and barber shops in Pakistan.
"We do not take any pressure and I have also explained my policy to US President Bush that we believe in dialogue and want development, health, education and to eliminate terrorism from the country."
Gilani was in Peshawar on Saturday but insisted that his trip was not related to the military operation.