Taliban insurgents killed at least 132 people, most of them children, after storming an army-run school in Pakistan on Tuesday in one of the country's bloodiest attacks in recent years.

"It may rise," said Bahramand Khan, director of information for the chief minister's secretariat, as the army was launching a final assault on the remaining militants still holding scores of children hostage. At least 245 others have been injured.

The Pakistani military said four Taliban militants had been killed at a school they attacked in the city of Peshawar on Tuesday, and that they were searching for remaining gunmen.

"Remaining clearance in progress," the military said in a tweet.

Witnesses described how a huge blast shook the Army Public School in the northwestern city of Peshawar and gunmen went from classroom to classroom, shooting children.

Distraught parents thronged the city's Lady Reading Hospital in the wake of the attack, weeping uncontrollably as children's bodies arrived, their school uniforms drenched in blood.

Irshadah Bibi, 40, whose 12-year-old son was among the dead, beat her face in grief, throwing herself against an ambulance.
"Oh God, why did you snatch away my son? What is the sin of my child and all these children?" she wept.

A security official told AFP that hundreds of students and staff were in the school when the attack began, though according to the military the bulk of them have been evacuated.

Militants came in army uniform

The attack began around 10.30 am when a group of at least six Taliban miltants, reportedly in military uniforms, entered the school.

A spokesperson for a faction of the Tehreek-e-Taliban Pakistan said the gunmen had been ordered to shoot older students at the school in the city of Peshawar.

TTP spokesman Muhammad Khorasani told AFP there were six attackers. "They include target killers and suicide attackers. They have been ordered to shoot the older students but not the children," he said.

"It's a revenge attack for the army offensive in North Waziristan," he said, referring to an anti-Taliban military offensive that began in June.

The attack comes as the Pakistani military wages a major offensive against Taliban and other militants in the tribal area of North Waziristan

Taliban opened fire on children

Mudassar Abbas, a physics laboratory assistant at the school, said some students were celebrating at a party when the attack began.

"I saw six or seven people walking class-to-class and opening fire on children," he said. One student said soldiers came to rescue them during a lull in the firing.

"When we were coming out of the class we saw dead bodies of our friends lying in the corridors. They were bleeding. Some were shot three times, some four times," the student said.

"The men entered the rooms one by one and started indiscriminate firing at the staff and students

Several students escaped through the back gate. One of students who escaped told Dunya TV that fourth period was in progress when they heard firing.

"First we didn't know what has happened. But late an army officer told us to escape through back gate," he said.

Mushtaq Ghani, provincial information minister, said the militants entered through a graveyard which is adjacent to the school. The school is close to Saint Mary High School located at the start of Warsak Road which was also under threat for last couple of days.

Prime Minister Nawaz Sharif described the attack as a "national tragedy unleashed by savages". "These were my children. This is my loss. This is the nation's loss," he said.

Militants chose soft target

The school on Peshawar's Warsak Road is part of the Army Public Schools and Colleges System, which runs 146 schools nationwide for the children of military personnel and civilians. Its students are between the 10 and 18 years.

The schools educate the children of both officers and non-commissioned soldiers and army wives often teach in them.

TTP spokesperson Muhammad Khorasani said the attack was carried out to avenge Taliban fighters and their families killed in the army's offensive against militant strongholds in North Waziristan.

More than 1,600 militants have been killed since the launch of Zarb-e-Azb in June, according to data compiled by AFP from regular military statements.