A Muslim imam has resigned as a taxpayer-funded Australian Defence Force religious adviser after a senator told parliament he had signed a petition in favour of Islamist extremist group Hizb ut-Tahrir.

Sheikh Mohamadu Nawas Saleem quit his $717-a-day post last month, only days after Australian Conservatives Senator Cory Bernardi questioned how the government could justify employing someone who opposed democracy.

Former Iraq war veteran Bernard Gaynor, who launched a petition calling for Sheikh Saleem's removal as Defence imam, said the government was embarrassed.

'The government's been very quiet about the resignation,' he told Daily Mail Australia on Sunday.

'They've been running politically correct games with in the Defence Force and they're embarrassed by the scrutiny.'

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Sheikh Mohamadu Nawas Saleem last month quit his role a Defence Force religious adviser

The former Australian Defence Force imam signed a pro-Hizb ut-Tahrir petition in early 2015

Australian Conservatives Senator Cory Bernardi raised the sheikh's support for Hizb ut-Tahrir

Former Iraq war veteran Bernard Gaynor campaigned for the sheikh's removal via a petition

Defence Personnel Minister Dan Tehan announced late last month Sheikh Saleem had resigned from the Religious Advisory Committee to the Services, which advises the Australian Defence Force.

His spokesman declined to detail the circumstances of the resignation in the wake of Liberal defector Senator Bernardi's speech to parliament.

Mr Tehan's short-lived predecessor Stuart Robert appointed Sheikh Saleem in June 2015 to his $717 a day role as a religious adviser.

Four months earlier, in February 2015, Sheikh Saleem added his name to a petition opposing then prime minister Tony Abbott's plan to ban Hizb ut-Tahrir in Australia.

The petition argued Hizb ut-Tahrir, which supports Sharia law and has a constitution backing the death penalty for ex-Muslims, had never committed terrorist acts in Australia.

Defence Personnel Minister Dan Tehan announced the sheikh's resignation late last month

Defence Personnel Minister Dan Tehan announced the sheikh's resignation in a media release

Sheikh Mohamadu Nawas Saleem was paid $717 a day to advise Defence on religious issues

But the group's Islamist ideology is so extreme it is banned in Germany, The Netherlands, Russia and a range of Muslim-majority nations including Indonesia Pakistan, Bangladesh and even Saudi Arabia.

Mr Tehan's media statement, published on June 23, did not condemn Sheikh Saleem's association with a petition defending Hizb ut-Tahrir.

'The government has always accepted the right of any member of the RACS to express their views according to their religious faith, but, as a matter of course, does not always agree with them,' he said.

'The government acknowledges Sheik Saleem's contribution to the RACS on behalf of his community.'

Sheikh Saleem signed a petition in 2015 opposing a plan to ban Hizb ut-Tahrir in Australia

Attorney-General George Brandis rejected a call in May to ban Hizb ut-Tahrir in Australia

Mr Gaynor, who served as an Iraq war intelligence analyst in 2008 and 2009, said a Muslim imam who signed a petition in favour of Hizb ut-Tahrir was bound to support Sharia law.

'An imam by virtue of his appointment and position will promote Sharia law,' he said.

The war veteran ran as an Australian Liberty Alliance candidate last year and last month launched a petition calling for Sheikh Saleem's removal.

It amassed 13,000 signatures.

In May, federal Attorney-General George Brandis rejected a call to ban Hizb ut-Tahrir, despite its recent calls for ex-Muslims to be killed and its advocacy of domestic violence.

Daily Mail Australia has been unable to contact the sheikh who is on the board of Imams Victoria.