The confrontations have left 45 pro-Taliban fighters dead and 11 Pakistani troops dead, Pakistan's military information office said on Saturday.

The wave of violence started when pro-Taliban fighters abducted 35 Pakistani policemen, following the arrest of six fighters, including two Taliban commanders, by Pakistan security forces.

Thirty-four civilians have died and 70 have been seriously wounded in the clashes, as shells and mortars hit houses, gardens and even a golf course.

At least 12 civilians, including seven members of the same family were killed on Thursday, a day after five soldiers and 25 fighters were killed in a gun battle sparked by an attack on a security checkpoint.

Residents said shells hit a house in the Deolai area of Swat on Thursday, killing five children and their parents.

"There had been heavy shelling overnight and when we woke up in the morning we saw Fasihul Ehsan's house destroyed, and when rubble was removed all the seven people in the house were dead," Jehanzeb Khan, a relative, told the AFP news agency on Friday.

A man was also killed in the crossfire between fighters and security forces at a golf course in the town of Kabal, officials said on Thursday.

In another instance, mortars fired from a Pakistani force helicopters landed on a civilian house on Friday.

"My son was killed in the shelling and some of my family members were wounded. My son is no longer with me and I feel like everything I have is gone.

"I want to ask the government, for god sake, please don't kill our women and children, please don't destroy our houses because you can't hit the exact targets you are after," the father of the boy said.

Hamid Karzai, Afghanistan's president, told a summit of South Asian leaders, which included Yousef Raza Gilani, Pakistan's prime minister, on Saturday that "terrorism" was gaining strength across the border in Pakistan.

"In Pakistan, terrorism and its sanctuaries are gaining a deeper grip as demonstrated by the tragic assassination of shaheed [martyr] Benazir Bhutto.

"While existing on the absolute fringes of our tolerant and peace loving societies, terrorists in our region receive institutional nurturing and support," he said.

"It is this embedded nature of terrorists that make it a much more sinister threat."

Relations between Afghanistan and its Pakistan have sharply deteriorated in recent months with Afghan officials repeatedly accusing Pakistani agents of secretly backing Taliban insurgents fighting Afghan and foreign troops on Afghan soil.

Pakistani forces have used helicopter gunships to pound Taliban fighter positions, while Taliban fighters set fire to government buildings, including two girls' schools on Thursday night, they said, threatening to target further government-linked installations.

Haji Muslim Khan, the spokesman for one of the largest pro-Taliban groups in the Swat valley, said that the trend would continue throughout Pakistan.

"Who killed the innocent people they are bombing and they are shelling from helicopters? It is the Pakistani army," he told Al Jazeera.

"I don't want America in my country and I don't want our soldiers to work for America and I want the rules and regulations of Islamic Sharia.

"Our government are following rules and regulations of America and we want to change it."

The warning follows a statement by Maulana Fazlullah, the Pakistan Taliban's leader in the Swat valley with a four million rupee ($56,000) bounty on his head, that the group has an army of suicide bombers that could strike across the country at any moment.

He told Al Jazeera that the Taliban has the capacity to take control of the entire Swat valley.

The intense fighting has brought a two-month-old peace deal between the Pakistani government and pro-Taliban fighters in the former tourist region to the brink of collapse.

Zahid Hussain, an expert on Pakistani religious groups, told Al Jazeera that the deal was born of failure.

"I think from the beginning it was very clear that it would not work," he said.

"While the deal was signed in May, there has not been a cessation of hostilities, and I think this period only displayed the fighters' capability to further arm and organise themselves."

Under the May peace deal, the Pakistan government agreed to gradually pull out troops and introduce an Islamic justice system.

In exchange, the Taliban said they would halt attacks and surrender arms.

In an exclusive interview with Al Jazeera's James Bays, General David McKiernan, commander of the International Assistance Security Force (Isaf), said: "[Violence] largely emanates from tribal sanctuaries across the border in Pakistan that allow the freedom of movement of insurgents into Afghanistan.

"My mandate as a Nato commander stops at the border. ... You asked me, is it frustrating that organisations such as the Taliban and al-Qaeda exist in sanctuaries across the border? - Absolutely frustrating."

Amid the heavy period of fighting, US television channel CBS said it had obtained an intercepted letter from a Pakistani Taliban commander urgently requesting a doctor to treat Ayman al-Zawahiri, al-Qaeda's deputy leader, following an attack in northwest Pakistan last week.

A senior military official based in the area said he was checking the CBS report.

"We have seen the media report that al-Zawahiri was killed or wounded in the July 28 strike. We are investigating the authenticity of the report," the official said.

Major General Athar Abbas, the chief Pakistani military spokesman, said that Pakistan's military had no information about the report.

"There is no evidence or information in this regard. We have no reliable information," told the AFP news agency on Saturday.

CBS said the letter, written by Baitullah Mehsud, a Pakistani Taliban leader, dated July 29 carried his seal and signature, saying Zawahiri was in "severe pain" and his "injuries are infected".

Mountainous Swat was a thriving tourist resort known as the "Switzerland of Pakistan" until last year, when Fazlullah launched an armed campaign to enforce Sharia law in the region.

Civilians have felt the force of fighting in the Swat Valley [AFP]