Hundreds of Islamist militants face death by hanging after Pakistani authorities said they plan to carry out a massive number of executions following the Taliban massacre in Peshawar.

Islamabad ended a six-year moratorium on the death penalty in terrorism-related cases, after 149 people, including more than 130 children, were slaughtered in an attack at an army-run school last week.

Six militants have been hanged in the last few days, with government officials now telling AFP they plan to execute another 500 in the coming weeks.

Several human rights groups, including the United Nations, have condemned Pakistan over the executions.

UN human rights spokesman Rupert Colville said: "To its great credit, Pakistan has maintained a de facto moratorium on the death penalty since 2008.

"We urge the government not to succumb to widespread calls for revenge, not least because those at most risk of execution in the coming days are people convicted of different crimes."

Pakistan's decision to remove the death penalty ban comes as political and military leaders across the nation vow to end homegrown terrorism.