The Taliban mastermind behind the carnage in a Peshawar army school has vowed more attacks if Pakistani forces do not scale down the anti-terror operations.

Umar Mansoor, the senior Taliban commander, who reportedly oversaw the Peshawar siege, said the school attack was "revenge" for the army's campaign against the militants.

In a nearly-two-minute video posted on the website of Tehreek-i-Taliban Pakistan (TTP), the official name of Pakistan Taliban, the senior militant with a chest-length beard who is nicknamed "slim", said: "If our women and children die as martyrs, your children will not escape. We will fight against you in such a style that you attack us and will take revenge on innocents."

Pakistani intelligence authorities were believed to have intercepted communication between Mansoor and Taliban militants, while the seven-hour siege was under way, guiding the perpetrators.

Investigators say Mansoor is also referred to as Khalifa Umar and Umar Narey.

At least six Taliban fighters interviewed by Reuters have confirmed that Mansoor, a close ally of TTP leader Mullah Fazlullah, was the mastermind behind the Peshawar attack.

One TTP member said: "He strictly follows the principles of jihad. He is strict in principles but very kind to his juniors. He is popular among the juniors because of his bravery and boldness."

Following the school massacre in which nearly 140 people, many of them children, were killed, Pakistan authorities have stepped up the offensive against the militants. The government has also upheld the death penalty for terrorists.

Earlier, there were also fears that Taliban might stage a massive jail-break to spring high-profile prisoners on death row.