ISLAMABAD (AFP) - Pakistan's military chief on Thursday signed death warrants for six militants on death row after the government ended a moratorium on capital punishment in terror-related cases, the military said.

"COAS (Chief of Army Staff) today signed death warrants of 6 hardcore terrorists (pending execution) convicted by FGCM in accordance with law," military spokesman Major General Asim Bajwa tweeted.

Security officials said the six were convicted by a military court and were awaiting execution.

The announcement came hours after the government warned prison officials of a possible jailbreak in the restive north-west province of Khyber-Pakhtunkhwa following the end of the moratorium.

It is not clear when the executions will be carried out, but a senior security official said the six would be hanged "within days".

Prime Minister Nawaz Sharif announced on Wednesday an end to the moratorium on the death penalty in terror-related cases after a Pakistani Taleban massacre at a military-run school killed 148 people, mostly children.

The assault in the northwestern city of Peshawar is the deadliest ever terror attack in Pakistan and has shocked the nation.

Political and military leaders have vowed in response to wipe out the home-grown Islamist insurgency that has killed thousands of ordinary Pakistanis in recent years.

Pakistan imposed a de facto moratorium on civilian executions in 2008, though hanging remains on the statute book and judges continue to pass the death sentence.

Only one person has been executed since then, a soldier convicted by a court martial and hanged in November 2012.

Rights campaign group Amnesty International estimates that Pakistan has more than 8,000 prisoners on death row, most of whom have exhausted the appeals process.