Turkey has the names of approximately 420 suspected Australian jihadists on a watch list it is using to block foreign fighters from travelling through its territory.

Key points: 21 suspected Australian foreign fighters deported from Turkey since 2015

21 suspected Australian foreign fighters deported from Turkey since 2015 Three Australians detained, including IS propagandist Neil Prakash

Three Australians detained, including IS propagandist Neil Prakash Turkey begins extradition process to send Prakash home

Speaking to the ABC, a senior Turkish official also said the country wanted to extradite notorious jihadist Neil Prakash back to Australia to face trial.

Turkey's "no entry" list is used to stop foreigners from entering Turkey, and is the result of intelligence from Turkey, Australia and more than 100 other countries.

It reveals international intelligence agencies have concerns about a significantly greater number of suspected Australian jihadists than previously known.

The evolution of the list is a window on the international effort to stop the flow of jihadists to Syria and a reflection of how those efforts initially lagged behind the flood of foreign fighters.

The number of Australians on the list grew from just 90 in 2014, with more than 180 added in 2015 and more than 150 added last year, according to a senior Turkish official who spoke on condition of anonymity to discuss intelligence-related matters.

As a result of the list, Turkey has deported 21 suspected Australian foreign fighters over the past two years, the official said.

Around half of them were sent back to Australia, but the rest were sent to other countries, underlining concern about the geographic spread of Australia's suspected jihadists.

Most were deported in 2015 as Australian Government efforts to stop would-be fighters from travelling, including cancelling their passports, were still ramping up.

Turkey's "no entry" list is part of an international counter-terrorism effort that began in 2010, grew in importance after the Syrian rebellion transformed into a civil war in 2011 and 2012, and gained real momentum after the Islamic State group seized swathes of Syria and Iraq in 2013 and 2014.

Australia's Justice Minister Michael Keenan would not comment on details of the list but told the ABC Turkey is a "friend and ally".

"We've got very good intelligence cooperation, so we will work with them to enhance their security," he said.

"Where we have information that might be useful to them then we would certainly share it and obviously we would expect the same."

That cooperation is proving even more crucial as the so-called caliphate collapses under attack from Iraqi Government forces, Western-backed militias and bombardment and IS members try to leave the conflict zone.

The most notorious Australian in Turkish custody is IS propagandist Neil Prakash. But a senior Turkish official has told the ABC two other Australians, detained in 2016, are also still in custody.

One of them has refused contact with Australian authorities. Further details could not be confirmed.

Prakash admits to being IS member

Neil Prakash says he regrets joining the Islamic State group. ( ABC News )

Turkey has begun proceedings to extradite Prakash, based on allegations from Australian authorities who accuse him of violating a raft of counter-terror laws.

The ABC understands the alleged offences include "membership of a terrorist organisation", "advocating terrorism", "providing support to a terrorist organisation" and "incursions into foreign countries with the intention of engaging in hostile activities".

However, recruiting for IS is not mentioned in the warrant.

Crucially, in a statement made to Turkish investigators less than 16 hours after he was detained on October 24 last year, Prakash admits to being a member of IS and says he regrets joining them. Turkey is prosecuting him for being a member of a terrorist organisation.

In what could prove a breakthrough for Australian authorities, the senior Turkish official said the prosecution was running in parallel to the extradition proceedings and Turkey would prefer for Prakash to be tried in Australia.

"The Turkish Government is very aware of our interest in this case. If we were to prosecute anybody for these crimes, and I won't comment on the individual … the penalties in Australia are as severe as they can be — life imprisonment," Mr Keenan said.

In Prakash's statement, obtained by the Guardian newspaper, he maintains he is a Cambodian national.

He makes no mention of his propaganda activities for IS and, while he was thought dead following an airstrike near Mosul in Iraq, he claims to have been injured only while fighting a Kurdish militia at Kobane in Syria.

Turkey views the Kurds as a terrorist group and his statement may have been calculated to curry favour with the Turks.

Prakash 'threat to Turkish national security'

Prakash does, however, describe transiting into Syria via a radical group known as Ahrar al Sham — a path several Australian IS recruits followed as IS grew in strength.

Who is Neil Prakash? Neil Prakash, 27, is of Fijian-Indian and Cambodian background, and attended Melbourne's controversial Al-Furqan Islamic Centre after converting

Neil Prakash, 27, is of Fijian-Indian and Cambodian background, and attended Melbourne's controversial Al-Furqan Islamic Centre after converting He is believed to have left for Syria in 2013, where he changed his name to Abu Khaled al-Cambodi and was put on a US kill list

He is believed to have left for Syria in 2013, where he changed his name to Abu Khaled al-Cambodi and was put on a US kill list Prakash was linked to several Australian-based attack plans and calls for lone-wolf attacks against the US

Prakash was linked to several Australian-based attack plans and calls for lone-wolf attacks against the US He has also appeared in IS propaganda

He has also appeared in IS propaganda Paul Maley, the national security editor of The Australian newspaper, said Prakash was "a lonely lost sort of a guy, he was a gang member, he had a problem with drugs, he was a failed hip hop artist"

The senior Turkish official says he was detained following an Australian alert stating he was in Syria near the border and possibly planning to cross over.

The alert was accompanied by other information, possibly derived from signals intelligence, which helped track and detain him. He is considered a "threat to Turkish national security".

Turkish authorities have been stung in the past by criticism they failed to stop jihadists entering Syria, especially in the early years of the civil war when tens of thousands of foreign fighters crossed their border.

They argued they needed the names of suspects and other cooperation from the home countries of suspects to stop the flow.

Intelligence agencies were slow to share, but additions to the list picked up pace as the seriousness of the jihadist threat became obvious.

Australia's liaison, officially stewarded by two Australian Federal Police agents, is highly valued in Ankara, with the senior Turkish official comparing it favourably to cooperation with European Union nations that grapple with much larger foreign fighter communities.

The official said more than 52,000 names were on Turkey's list, which is much larger than the total number of suspected foreign fighters in Syria and Iraq.