Prakash branded a 'coward' for fleeing IS

Australia's most wanted terrorist Neil Prakash apparently fled Iraq because he was a "coward" who couldn't handle bomb attacks led by the Iraqi army.

Amarnath Amarasingam, who co-directs a study of western foreign fighters at Canada's University of Waterloo, says the claim was made by an Islamic State fighter to him during a recent online chat.

Melbourne-born Prakash was believed to have been killed during a bomb attack on Mosul, an ISIS stronghold in Iraq's north, in April.

But the IS recruiter was recently arrested in Turkey after having crossed the border using fake identity documents.

Amarasingam used Twitter to post a transcript of his conversation with the unnamed IS fighter, who said Prakash "couldn't handle war anymore " and had left ISIS.

"He is a westerner after all," the IS fighter wrote.

The IS fighter said he had heard speculation that part of Prakash's decision to flee was because he was part of the extreme hazimi sect within ISIS that is made up of followers of Saudi cleric Ahmed al-Hazimi.

"But the main thing is cowardice ... facing airstrikes is not easy," he said.

Prakash has been linked to a failed Melbourne plot to behead a police officer on Anzac Day lsat year and Numan Haider, an 18-year-old who was killed after stabbing two police officers a year earlier.

Australian authorities are hoping to have him extradited from Turkey to face court on home soil.

But Australia may have to wait in line as intelligence agencies in the European Union, United States and Israel make their case to question Prakash.

Prime Minister Malcolm Turnbull has previously described Prakash as the most senior Australian operator in IS.

He had been an effective propagandist and recruiter for ISIS, having been a regular at the Al-Furqan centre in Melbourne's south before leaving for Syria in 2013.

The Sydney Morning Herald reported that Prakash's use of social media to communicate with other foreign fighters in recent months could have led to his arrest in Turkey.