ISLAMABAD: Pakistan Prime Minister Nawaz Sharif has urged Afghan President Hamid Karzai to help stop militants escape a major military offensive, as jets pounded Taliban hideouts in North Waziristan tribal region for a third day Tuesday.

Sharif asked his Kabul counterpart to seal their porous border along a mountainous tribal area where the Pakistani army has deployed troops and tanks in a long-awaited crackdown on insurgents.

Pakistan's army launched the offensive, named Zarb-i-Azb on Sunday, a week after an attack on Karachi airport killed dozens and marked the end of a troubled peace process.

Exodus of militants from the area had been a concern ahead of the operation, with residents and officials reporting that the majority of Taliban and foreign fighters had fled to eastern Afghanistan.

Pakistan's Foreign Office spokeswoman Tasnim Aslam said Sharif had requested Karzai to help stop the flow of people.

"Prime Minister Nawaz Sharif called Hamid Karzai last night to request him for the closure of Afghan border to avoid exit of militants to Afghanistan from Pakistan during the military offensive,” she told AFP.

"The message was earlier conveyed via military sources and Afghan authorities were also requested for an action against militants' sanctuaries in Afghanistan which are being used for attacks inside Pakistan.

"I am not aware about the response of Mr. Karzai to these requests,” she added.

Thousands of people have already fled across the border into the Gorbaz district of Afghanistan's Khost province, according to provincial government spokesman Mobarez Mohammad Zadran, and are being provided with food and aid.

Sharif had earlier said the offensive would usher in peace while militants vowed revenge and warned foreign firms to leave the country.

The army has deployed tanks, ground troops and jets in the area but has encountered relatively little resistance so far, with the majority of alleged militant deaths resulting from air strikes.

Earlier in April this year, the border between Pakistan and Afghanistan had also been sealed owing to the presidential election held in Afghanistan.