AFP/Islamabad

A Pakistani court has issued an arrest warrant for a hardline Islamic cleric who suggested the massacre of school children in country's worst ever terror attack was understandable, after he allegedly threatened people criticising him.

Maulana Abdul Aziz, the pro-Taliban cleric and head of the Red Mosque in capital Islamabad has been accused of threatening civil society activists, who this week staged several demonstrations outside the mosque, a police official and a spokesman for the mosque told AFP.

The protests were staged to denounce Aziz, who refused to condemn the massacre on a television talk-show.

Later Aziz effectively told worshippers the attack in Peshawar, which left around 150 people dead -- mainly children, was a justifiable reaction to the army's "un-Islamic" operation against militants in the North Waziristan tribal district.

"O rulers, O people in power, if you will commit such acts, there will be a reaction," he told worshippers in a sermon last week, prompting further protests accusing him of being a Taliban sympathiser.

"Police have received the court order and we are trying our best to implement it," a police official in capital Islamabad told AFP, requesting anonymity as he was not authorised to talk to media.

Hafiz Ihtesham Ahmed, a spokesman for the Red Mosque accused civil society activists of pressurising police to register a case against Aziz. 

"This case has no grounds, so we will resist any move to arrest Maulana Abdul Aziz," Ahmed told AFP.

Pakistan has described the bloody rampage in Peshawar as its own "mini 9/11", calling it a game-changer in the fight against extremism.

The Tehreek-e-Taliban Pakistan (TTP) claimed the assault as revenge for an ongoing military offensive against its strongholds in the tribal northwest.

The Red Mosque, which stands a stone's throw from the parliament buildings in the centre of the capital, was the scene of a week-long military siege against radicals which left more than 100 people dead in 2007.

Earlier this month female students affiliated with the Red Mosque issued a video statement praising the Islamic State group and calling on it to avenge the death of Osama bin Laden.

The women belong to the Jamia Hafsa seminary which in April named its library in honour of the slain Al-Qaeda leader.