ISLAMABAD (AFP) - Pakistan's prime minister rejected appeals by four militants sentenced to death in the Peshawar school massacre, saying on Thursday (Nov 19) that those behind the country's deadliest-ever terror attack deserved "no mercy".

With the anniversary of the Dec 16, 2014 attack approaching, Prime Minister Nawaz Sharif directed President Mamnoon Hussain to reject the mercy petitions appealing the executions.

The massacre - in which Taleban gunmen coldly slaughtered more than 150 people, most of them children, at an army-run school in the north-western city - shocked and outraged a country already scarred by nearly a decade of attacks.

It prompted a crackdown on extremism, with the establishment of military courts and the resumption of capital punishment after a six-year moratorium.

In August, after a trial that took place behind closed doors, the army announced that six militants linked to the assault would be executed, while a seventh was handed a life sentence.

It was not clear if the remaining two facing execution had also filed mercy petitions.

"Prime Minister Muhammad Nawaz Sharif has advised the president to reject the mercy petitions of all four convicted terrorists of Army Public School Peshawar terrorist attack," the prime minister's office said in a statement.

"The Prime Minister said that Pakistan has been changed after the Peshawar tragedy," the statement continued.

"The brutal and merciless killings of our children convinced us that the perpetrators of such crimes do not deserve any mercy... The death sentence awarded to the four terrorists, in fact, was the will of the entire nation."

Mr Sharif said by rejecting the mercy petitions he was "honouring the promise made to the families" of the children killed in the tragedy, according to the statement.

No date for the executions has been announced.