At least 100 people, most of them children, have died in an attack by Taliban fighters on a military-run school in Peshawar in the northwest of Pakistan, according to reports. 

Around half-a-dozen Taliban militants wearing military uniforms stormed the school this morning, with reports claiming that upwards of 80 students were among those killed.

Gunfire and helicopters were heard outside the school as Pakistani troops surrounded the building and ambulances carried the wounded to hospital.

The army said that the majority of the school’s 1,500 students and teachers have been evacuated, but it is still unclear just how many have got away.

“Rescue operation by troops under way. Exchange of fire continues. Bulk of student(s) and staff evacuated. Reports of some children and teachers killed by terrorist,” the army said in a brief English-language statement.

The attack began this morning, with the gunmen entering the school and shooting at random, according to police reports. Army commandos quickly arrived at the scene and exchanged fire with the gunmen.

The Tehreek-e-Taliban Pakistan (TTP) claimed responsibility for the attack.

It comes as the Pakistani military launched a major offensive against the Taliban and other militants in the tribal regions of Pakistan. The Pakistani Taliban, who are fighting to topple the government and set up a strict Islamic state, have vowed to step up attacks against Pakistani targets in response.

Malala Yousafzai, who was herself shot in the face by the Pakistani Taliban while travelling into school, said she was “heartbroken” by the attack.

The Nobel Prize-winning campaigner said: “Innocent children in their school have no place in horror such as this.

“I condemn these atrocious and cowardly acts and stand united with the government and armed forces of Pakistan, whose efforts so far to address this horrific event are commendable. I, along with millions of others around the world, mourn these children, my brothers and sisters - but we will never be defeated.”

Prime minister David Cameron today added that the violence was, “deeply shocking. It’s horrifying that children are being killed simply for going to school”.