Security forces killed dozens of militants along the Afghan border on Friday, the army said, as violence escalated sharply along the frontier following Taliban assaults on two military outposts this week.

A group of militants attacked a fort at Ladha with small arms and rockets, drawing artillery, mortar and small arms fire from security forces, who killed between 50 and 60 militants and forced the rest to disperse, an army statement said.

Also Friday, a convoy of security forces came under attack near the village of Chakmalai, sparking a one-hour firefight. The army estimated that between 20 and 30 militants were killed. Four troops were wounded.

It was not immediately possible to independently confirm the casualty figures. Travel in the volatile region is dangerous and phone links are poor.

Pakistan's military is struggling to respond to a surge in attacks on security forces in the lawless, mountainous area, where top Al Qaeda leaders are thought to be hiding.

Taliban and Al Qaeda militants based in the volatile tribal region are blamed for a series of homicide attacks including the Dec. 27 gun and bomb attack that killed Benazir Bhutto, the secular opposition leader who had vowed to battle Islamic extremism.

Earlier this week, hundreds of troops loyal to Taliban commander Baitullah Mehsud attacked two military forts in South Waziristan, highlighting rising militant control of the area.

President Pervez Musharraf has blamed Mehsud for many of the more than 20 homicide attacks in Pakistan over the past three months that have left over 400 dead. He also masterminded the brazen capture of 213 Pakistani soldiers last August.

Pakistan has said — and the CIA also believes — that the Pakistani militant was behind Bhutto's assassination, according to a U.S. intelligence official who spoke on condition of anonymity because of the sensitivity of the matter. Mehsud has denied involvement in her death.

Earlier Friday, a medic in Chakmalai reported heavy fighting after a large number of infantrymen moved into the area under the protection of helicopter gunships — although the army spokesman denied it had launched an offensive. The medic, Alam Sher, said two people were killed close to the village.

"Since early morning I have been hearing gunshots and explosions, and I am receiving calls from local people to come to provide medical aid to the injured," he said, adding that fierce gunfire prevented the retrieval of the two bodies.

An intelligence official in the region confirmed fighting in Chakmalai and said the army and paramilitary Frontier Constabulary were trying to clear the area of pro-Taliban insurgents. He asked not to be identified because he was not authorized to speak to the media.

On Thursday, the army reported Cobra gunships fired on two vehicles carrying rebels, killing eight.

Musharraf first deployed the army in Pakistan's semiautonomous tribal regions along the frontier in late 2001 to chase down Al Qaeda militants fleeing the U.S.-led invasion of Afghanistan.

Nearly 100,000 soldiers are now in the area. While Western officials have reported some curbing of cross-border attacks into eastern Afghanistan in recent months, Pakistani forces have failed to quell the worsening Islamic insurgency on its own soil.

In other violence, a suspected Sunni extremist blew himself up inside a Shiite mosque, killing 11 people in the northwestern city of Peshawar. The strike late Thursday wounded 25 people, including a prominent Shiite cleric, ahead of Ashoura, a Shiite festival often is scarred by sectarian violence. Sunnis outnumber Shiites by about four to one in this overwhelmingly Islamic nation of 160 million people.

The attack added to tensions in the country ahead of Feb. 18 parliamentary elections that many predict will weaken Musharraf's grip on power eight years after he seized control of the nuclear-armed nation in a military coup.

In a related development, two Sunni extremists on death row for a 2004 attack on a procession that killed 42 Shiites were found missing from their cell Friday in Quetta in the southwest province of Baluchistan, said city police chief Rehmatullah Niazi.

There was no sign of forced exit and several jail officials were being questioned over the escape, he said.

"Their escape in a sensitive month is very dangerous," he said. "We have launched an operation to arrest them."