Parents urged to watch jihad signs

Death cult: Islamic State has attracted recruits from around teh world. Picture: AP

The Federal Government is urging parents to take greater interest in their children's online activity to ensure they are not brainwashed by the Islamic State "death cult".

The warning came after two Australian-born teenage boys were stopped at Sydney Airport from travelling to Turkey from where they planned to join Syrian-based radical Islamists.

"These two young men aged 16 and 17 are kids not killers and they shouldn't be allowed to go to a foreign land to fight then come back to our land eventually more radicalised," Immigration Minister Peter Dutton said.

Customs and Border Protection officials at Sydney Airport were alerted to the teenagers' motive for travel after finding suspicious items in their luggage.

This included jihadist paraphernalia and a document advising on cover stories in the event of being stopped by border officials. Mr Dutton would not say who paid for the pair's return airline tickets.

"The availability of information over the internet of course is limitless and I would say to all parents, please do whatever you can to remain engaged with your children," he said.

"Traditionally, parents of teenage children have to worry about alcohol, drugs and driving - now there is an added threat of the information that is available to them over the internet, particularly if they are inclined to fight in a foreign land and then come back as a threat to our society."

Between 16,000 and 20,000 foreigners have become fighters in Syria and Iraq, with about 7000 having returned home.

Between 100 and 250 Australians have travelled to Syria and Iraq and about 90 are still there. Twenty have been killed. Security agencies are actively monitoring about 400 people in Australia.

Prime Minister Tony Abbott said no one could feel "entirely safe" as long as Islamic State existed and urged anyone tempted by its message to "block your ears".