Pakistan Prime Minister Nawaz Sharif has urged Afghan President Hamid Karzai to help stop insurgents from escaping a major military offensive.

Pakistan Prime Minister Nawaz Sharif has urged Afghan President Hamid Karzai to help stop insurgents from escaping a major military offensive.

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.

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.

Karzai's office later issued a statement asking Pakistan to take all steps to reduce civilian casualties, adding that Sharif would soon send a "special envoy" to discuss the issue.

"Afghanistan is ready for any cooperation so that terrorists' sanctuaries that exist on the other side of the Durrand line be eliminated and that attacks on Afghanistan stop," the statement added.

Fresh air strikes early Tuesday targeted three Taliban militant strongholds in Mir Ali town in North Waziristan and killed 13 alleged militants, three security sources said, raising the total insurgent death toll to 190.

The figure could not be independently confirmed and some residents who had escaped the area spoke of civilian casualties from aerial bombing before the operation was officially launched, as they awaited a break in the fighting to rescue relatives who remained behind.

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

An 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 the porous border area.