SYDNEY - An 18-year-old man from Queensland has joined Al-Nursa front, an al-Qaida's affiliate in Syria, the Australian Federal Police said on Friday.

Local media reports said the man, from Toowoomba, inland Queensland, fled Australia the al-Qaida's Syrian affiliate in April after tricking his parents into letting him leave.

Islamic Council of Queensland spokesman Ali Kadri told the Australian Broadcasting Commission he was surprised by the action, however many young Muslim men feel disenfranchised in their community.

"I would request politicians to watch what they say and be measured in their statements," he said, adding "The prime minister or the top ministers attacking Muslims makes them feel more marginalised and alienated."

Duncan Lewis, the head of Australia's domestic spy agency ASIO says Australian teenagers are becoming increasingly susceptible to propaganda, sometimes being "radicalised" within weeks.

"They are getting younger," Lewis said to Fairfax Media. " September last year we still had people in their 20s (being arrested) ... By Christmas it was turning down to late teens. Now we are talking about teens. So there is a trend downwards in terms of youth."