Abdul Aziz, who survived a 2007 military operation against militants hiding in the mosque when he was caught trying to escape wearing a burqa, said he can prove that the military operation was against the teachings of Islam.
"This operation in the North Waziristan is un-Islamic," Aziz said.
"I can debate this issue...Call scholars from abroad -- from India and Bangladesh -- and I will prove that this operation is un-Islamic," he said.
He has hypocritically expressed grief at the loss of life, and said the TTP's response to the military operation was understandable.
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The TTP has said the attack was a revenge for an ongoing military offensive against its strongholds in the tribal northwest.
The army has killed more than 1,700 militants since June in operations against the TTP and other militants in North Waziristan and Khyber tribal areas.
The cleric's reaction to the attack, drew protests from furious civil society members outside the mosque. They shouted slogans against the cleric.
The cleric, who has issued statements in favour of Islamic State terrorists group, has been preaching extremism in the heart of the Pakistani capital.
He has already wriggled himself out of several charges of murder, kidnapping, waging war on the State among others to the surprise of many.
The Red Mosque enjoys an iconic status among Pakistani extremists. The cleric has even named a library in his madrasa after Osama bin Laden.
The 2007 siege was triggered after its leaders sent students armed with sticks onto the city's streets to try and impose hardline Sharia laws.
Aziz's younger brother was also killed in the siege.