PESHAWAR, Pakistan - In the deadliest slaughter of innocents in Pakistan in years, Taliban gunmen attacked a military-run school Tuesday and killed 141 people - almost all of them students - before government troops ended the siege.

The massacre of innocent children horrified a country already weary of unending terrorist attacks. Pakistan's teenage Nobel Peace laureate, Malala Yousafzai - herself a survivor of a Taliban shooting - said she was "heartbroken" by the bloodshed.

Even Taliban militants in neighboring Afghanistan decried the killing rampage, calling it "un-Islamic."

If the Pakistani Taliban extremists had hoped the attack would cause the government to ease off its military offensive that began in June in the country's tribal region, it appeared to have the opposite effect. Prime Minister Nawaz Sharif pledged to step up the campaign that - along with U.S. drone strikes - has targeted the extremists.

"The fight will continue. No one should have any doubt about it," Sharif said. "We will take account of each and every drop of our children's blood."

Taliban fighters have struggled to maintain their potency in the face of the military operation. They vowed a wave of violence in response to the operation, but until Tuesday, there had been only one major attack by a splinter group near the Pakistan-India border in November. Analysts said the school siege showed that even diminished, the extremist group still could inflict horrific carnage.

The rampage at the Army Public School and College began in the morning when seven extremists scaled a back wall using a ladder, said Maj. Gen. Asim Bajwa, a military spokesman. When they reached an auditorium where students had gathered for an event, they opened fire.

A 14-year-old, Mehran Khan, said about 400 students were in the hall when the gunmen broke through the doors and started shooting. They shot one of the teachers in the head and then set her on fire and shouted "God is great!" as she screamed, added Khan, who survived by playing dead.

From there, they went to classrooms and other parts of the school.

"Their sole purpose, it seems, was to kill those innocent kids. That's what they did," Bajwa said. Of the 141 people slain before government troops ended the assault eight hours later, 132 were children and nine were staff members. An additional 121 students and three staff members were wounded.

The seven attackers, wearing vests of explosives, all died in the assault. It was not immediately clear if they were all killed by the soldiers or whether they blew themselves up, Bajwa said.

The wounded - some still wearing their green school blazers - flooded into hospitals as terrified parents searched for their children. By evening, funerals were already being held for many of the victims as clerics announced the deaths over mosque loudspeakers.

The government declared three days of mourning for what appeared to be Pakistan's deadliest attack since a 2007 suicide bombing in the port city of Karachi killed 150 people.

"My son was in uniform in the morning. He is in a casket now," wailed one parent, Tahir Ali, as he came to the hospital to collect the body of his 14-year-old son, Abdullah. "My son was my dream. My dream has been killed."

One of the wounded students, Abdullah Jamal, said he was with a group of eighth, ninth, and tenth graders who were getting first-aid instructions and training with a team of army medics when the violence became real. Panic broke out when the shooting began.

"I saw children falling down who were crying and screaming. I also fell down. I learned later that I have got a bullet," he said, speaking from his hospital bed.

A little more than 1,000 students and staff were registered at the school, which is part of a network run by the military, although the surrounding area is not heavily fortified. The student body is made up of both children of military personnel and civilians.

Most of the students appeared to be from civilian families rather than children of army staff, said Javed Khan, a government official. Analysts said the extremists likely targeted the school because of its military ties.

In a statement, Taliban spokesman Mohammed Khurasani claimed responsibility for the attack, saying it was retribution for the military's operation in nearby North Waziristan, the northwestern tribal region where the group's fighters largely have been based.

"We targeted their kids so that they could know how it feels when they hit our kids," Khurasani said.

All About the Pakistani Taliban

A look at the Pakistani Taliban, an extremist organization that has claimed responsibility for a deadly attack on a school in the northwestern city of Peshawar:

Who are the Pakistani Taliban?

The extremist group is made up of fighters who largely have been based in North Waziristan, a northwestern tribal region bordering Afghanistan. They have been battling government troops in the northwest since Pakistan aligned itself with the U.S.-led war in Afghanistan. But the Pakistani Taliban didn't officially form until 2007 as an umbrella organization that included various militant factions, all aligned against the government. In recent months, the organization has fractured amid a Pakistani military offensive and U.S. drone strikes that have raised tension in the ranks. Known as the Tehreek-e-Taliban Pakistan, or TTP, it is headed by Mullah Fazlullah, a militant commander who claimed responsibility for trying to kill education activist Malala Yousafzai in 2012. The teenager survived the shooting and won the Nobel Peace Prize.

What are its goals?

The TTP has vowed to overthrow the government and install a harsh form of Islamic law. The extremists are aligned with the Afghan Taliban - a group fighting U.S. and Afghan forces in Afghanistan - as well as al-Qaeda militants who also live in the rugged northwest. They have frequently attacked Pakistani troops, government targets, and civilians to help carry out their goals. Tens of thousands of people have been killed in the violence, but Tuesday's school assault was one of the deadliest in more than a decade of fighting.

What has Pakistan's government done?

Pakistan's military has carried out numerous operations in the tribal areas over the years, and more than 4,000 soldiers have been killed, with thousands more wounded. But many Pakistanis have tired of the operations and question their effectiveness. Prime Minister Nawaz Sharif, elected in 2013 partly on a platform of promising to negotiate an end to the violence, has tried for months to talk to the militants with little result. When militants attacked the Karachi international airport in June, the violence shocked the country. The government began an offensive in the militant hub of North Waziristan - the last remaining tribal area where the military had not launched an operation. Pakistan says it has killed more than 1,000 militants in the operation, which displaced hundreds of thousands of people.       - Associated Press

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