Australia police prevent 230 suspected militants, including three teenagers, from travelling to Middle East to fight for Isis

Two brothers, aged 16 and 17, were stopped at Sydney International Airport on suspicion they were headed for conflict in the Middle East earlier this month

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Counter-terror police in Australia have stopped up to 230 people – including three teenagers – suspected of trying to fly to the Middle East to fight with groups including Isis, officials have said.

The announcement comes after a 17-year-old boy was stopped at Sydney International Airport on suspicion he was headed for conflict in the Middle East, less than a week after two brothers, aged 16 and 17, were intercepted at the same airport on March 8.

The two siblings, who have not been named, were returned to their parents and were to be charged.

The 17-year-old boy stopped was also returned to his family, but remained under investigation, Border Protection Minister Peter Dutton has said.

Fears have been raised in Australia that Isis is luring teenagers to the Middle East, although experts have disagreed on why the militant group may have been so effective at recruiting in the country.

According to a London-based radicalisation think tank, between 100 and 250 Australians have joined Sunni militants in Iraq and Syria.

The International Centre for the Study of Radicalisation and Political Violence also estimates that about 100 fighters have come from the US – a country with a population 13 times bigger than Australia.

The militant group has also reportedly posted a step-by-step guide online informing would-be jihadists of how to leave Australia.

According to Sydney's The Daily Telegraph, the guide included advice on how to slip through security cracks and use an Isis support network.

It is believed the network was used by teenager Jake Bilardi, who flew from Melbourne last year to join Isis without alerting security agencies.

Jake Bilardi flew from Melbourne to join Isis in Iraq last year

The 18-year-old was reportedly killed in a suicide bomb attack in Iraq earlier this month.

Australian Prime Minister Tony Abbott has told Parliament that since counter-terrorism units were attached to eight airports in August, 86,000 people have been questioned, with 230 prevented from flying on suspicion they were headed to fight with groups including Isis in Iraq and Syria.

Mr Abbott said there was to be more investment on border secuity and countering extremism.

“It is absolutely critical that the people of Australia appreciate that the death cult is reaching out to vulnerable and impressionable young people,” he said. “The death cult is reaching out, seeking effectively to brainwash people online.”

Additional reporting by AP