An Islamist extremist who supports the killing of ex-Muslims has been invited to speak at Australia's most prestigious university on the existence of God.

Hizb ut-Tahrir spokesman Uthman Badar is appearing at the University of Sydney's Footbridge Theatre on Thursday night as part of a debate with atheist activist Dr John Perkins, who lost a relative in the 2002 Bali bombing.

The Sydney University Muslim Students' Association, who are the event organisers, described Mr Badar in glowing terms, only six months after Daily Mail Australia caught him on camera declaring capital punishment was an appropriate punishment for those who left Islam.

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Hizb ut-Tahrir spokesman Uthman Badar supports capital punishment for ex-Muslim apostates

'His arguments are quick, sharp and straight to the point - a must see at the debate this upcoming Thursday,' it says on its Facebook page.

Dr Perkins, who is also the president of the Secular Party of Australia, is going head to head with Mr Badar on the topic of whether science disproves the existence of God.

The economist said he feared for his safety but wanted to challenge Mr Badar on his policy of killing ex-Muslims and taking a literal interpretation of Islam.

'I'll ask him to renounce violence and I presume he won't,' Dr Perkins told Daily Mail Australia on Wednesday.

'He's very close to the edge of the law in advocating violence.'

Secular Party of Australia president John Perkins, an atheist, is worried for his personal safety

Dr Perkins, whose distant cousin Robert Thwaites was killed in the 2002 Bali bombings, is hoping the University of Sydney provides security, after he had to be escorted from the University of Western Sydney during a previous debate with Mr Badar.

'I hope they provide it,' he said. 'I'm not unaware that my own personal safety may be at risk.'

Mr Badar is a controversial figure who speaks on behalf of Hizb ut-Tahrir, which has a constitution calling for the establishment of an Islamic caliphate based on Sharia law.

Hizb ut-Tahrir debater Uthman Badar wants a global Islamic caliphate based on Sharia law

The Sydney University Muslim Students' Association is organising the debate on Thursday

In March, he told a forum in Bankstown in Sydney's south-west that ex-Muslims deserved death.

'The ruling for apostates as such in Islam is clear, that apostates attract capital punishment and we don't shy away from that,' Badar said in the presence of children.

An apostate is someone who decides to leave Islam.

Hizb ut-Tahrir is so extreme it is banned in a range of Muslim-majority nations, including Indonesia, Pakistan, Bangladesh and Saudi Arabia, along with The Netherlands and Germany.

Uthman Badar (left) and Wassim Doureihi are regarded as people who take Islam literally

However, Australian Attorney-General George Brandis has declined to ban the group in Australia on the grounds they haven't committed any violence atrocities in Australia.

Dr Perkins said Hizb ut-Tahrir was an example of a Muslim group that took a literalist interpretation of the Koran.

'I want to make the point that although they're called extremists, they are simply representing a literal interpretation of Islam,' he said.

'The idea that Islam is a moderate religion is completely false, is a fabrication.

'What they represent is actually the authentic Islam: Islamic State and Hizb ut-Tahrir are what you get.'

He is being joined by Secular Party of Australia vice president Ian Bryce.

Daily Mail Australia has contacted the University of Sydney for a response.