Australia's domestic spy agency the Australian Security Intelligence Organisation (ASIO) has cancelled the passports of 20 men from across western Sydney because of fears of their 'jihad mentality' and that there was a possibility of the men travelling abroad to participate in politically motivated violence.

In an exclusive, the Sydney Morning Herald reports that the move against the men came without warning. Some of the men found their passports had been cancelled or were deemed to have been ''invalidly obtained'' when they tried to leave Australia on holiday to Thailand, Bali and Saudi Arabia.

As reported earlier, the Sydney police had arrested two men on charges of attempting to help fighters in the Syrian Civil war. A 39-year-old was charged for being "actively involved in recruiting" Australian men and facilitating their travel to Syria, along with a 23-year-old who was arrested for attempting to travel to Syria for participation in the ongoing civil war. It was reported that the police were on the lookout for five others in the case.

Abu Bakr, 19, one of the men whose passport was cancelled by the ASIO told the SMH that he first came to know that the spy agency thought he would become a foreign fighter when he received a letter saying he was a threat to national security and asked him to surrender his passport.

''It is a 10-page letter saying I had a jihadi mentality ... I have never been approached by ASIO to talk about this,'' he said.

Claiming that he had no plans to travel overseas, Mr Bakr said his record was clear, shiny gold.

"I am not a criminal," he said.

Mr Bakr believes the only reason he was targeted was because he was outspoken about atrocities against Muslims.

Australia's intelligence agencies believe there are more that 100 Australians who are fighting overseas with groups such as Jabhat al-Nusra in Syria.

The report said a Brisbane man who carried out a truck bomb attack this year is thought to be the first Australian suicide bomber in Syria.