Most such groups have slaughtered civilians themselves, but the wave of outrage following the school attack is threatening the relative freedom they enjoy in Pakistan.
The country is home to a range of armed militant groups. Some, like the Pakistani Taliban, fight against the state. Others have cosier ties with the authorities who use them against India and to jostle for influence in Afghanistan.
Whether Islamabad moves against all of them equally will show whether the school massacre has finally spurred authorities to tackle militancy seriously, said Senator Afrasiab Khattak.
"They are all terrorists and the state has to clearly oppose them in all shapes and colours," he added.
"So far they have not done so," he said.
The Afghan Taliban, a group Pakistani jihadists look up to, were the first of the Sunni Islamist armed groups to denounce the school attack as unIslamic, despite often killing civilians themselves. An Afghan Taliban suicide bomber killed more than 50 people at a volleyball match last month.

Some Pakistani Taliban, including powerful splinter group Jamaat-ul-Ahrar, quickly sided with their Afghan patrons.
"Like them, we condemn the attack on the school and killing of innocent children," said spokesman Ehsanullah Ehsan. The group earlier claimed responsibility for an attack that killed more than 50 people last month at a border crossing to India.
Other condemnation came from sectarian or anti-Indian groups that are nominally banned in Pakistan but operate openly, sometimes under different names.
Afghanistan has long accused Pakistan of supporting the Afghan Taliban to try to maintain its influence in the region. Pakistan says Afghanistan is doing the same with the Pakistani Taliban in return.
An Islamabad-based analyst said the Afghan Taliban's condemnation could be intended to protect its Pakistan bases.
"Any group that still wants to maintain a working relationship with the Pakistani establishment has to denounce this attack," he said.
"They must distance themselves from (Pakistani Taliban leader Mullah) Fazlullah and the outrage around him," he added.
Another banned Pakistani group said it stood alongside the military in response to the attack.
"We strongly condemn the attacks on schoolchildren in Peshawar and believe that there is no religious, ethical or any other social reason for this cruel act," said Ghulam Rasool Shah, a deputy for Malik Ishaq, leader of the sectarian group Lashkar-e-Jhangvi.
"We stand with the Pakistan army and political leadership in this critical situation," he added.
The group was responsible for twin blasts in the city of Quetta last year that killed around 180 people, mostly civilians from a Shi'ite Muslim ethnic group.
Authorities were accused of inaction in response to those attacks, leading victims' families to stage a sit-in alongside the bodies of the dead on a main road for several days in protest.

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