PESHAWAR, Pakistan

- In the deadliest slaughter of innocents in Pakistan in years, Taliban gunmen attacked a military-run school yesterday 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 spree, 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 militants.

"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 yesterday, there has 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 militant group still could inflict horrific carnage.

The rampage at the Army Public School and College began in the morning when seven militants 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!, added Khan, who survived by playing dead.

"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. Another 121 students and three staff members were wounded.

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

President Obama said the "terrorists have once again showed their depravity."