The death toll from a militant attack on an army-run school in Pakistan’s northwestern province of Khyber Pakhtunkhwa has risen to around 130 including 126 children, officials say.

The incident occurred on Tuesday when a group of pro-Taliban militants wearing military uniforms stormed the school in the city of Peshawar.

“The attack started with the gunmen entering the school in the morning hours and shooting at random,” said police officer Javed Khan.

There was also a huge blast inside the building. Hundreds of students and staff were present at the school when the attack began.

The Tehreek-e-Taliban Pakistan (TTP) claimed responsibility for the attack, saying it was revenge for the army's continuing operation against militants in the North Waziristan tribal area which borders Afghanistan.

The Pakistani army runs 146 schools nationwide for the children of military personnel and civilians.

In June, the Pakistani army launched a major offensive against militant hideouts in North Waziristan Agency after a deadly militant raid on Karachi Airport ended the government’s faltering peace talks with pro-Taliban militants.

Pakistan’s army claims it has killed over 1,600 militants so far, while losing 126 of its own soldiers. However, rights groups say a large number of civilians are among those killed in the Pakistani army operations.

This comes as Pakistan's Inter-Services Intelligence is known as the main supporter of the Taliban.

The North Waziristan region serves as a major base for the Tehreek-e-Taliban Pakistan and the Haqqani network, which also targets US-led troops across the border in Afghanistan.