Australia said on Sunday it had stopped two teenage brothers at Sydney Airport believed to be heading to the Middle East to fight alongside jihadist groups, AFP reported.

Immigration Minister Peter Dutton said the two boys, aged 16 and 17 and from Sydney, had tickets to an undisclosed Middle Eastern country and raised the suspicions of customs officers on Friday night.

“These two young men… are kids, not killers, and they shouldn’t be allowed to go to a foreign land to fight and to come back to our shores eventually more radicalized,” Dutton was quoted as having told reporters.

“In some cases, these young people who are going off to fight in areas like Syria will be killed themselves and that’s a tragedy for their families, for their communities, and for our country,” he added.

The minister said a search of the boys’ luggage raised more questions about their trip and they were referred to the federal police’s counter-terrorism unit.

He said the two youths “had taken a very radical decision ultimately without the knowledge of their parents”.

“Their parents, as I understand it, were as shocked as any of us would be.”

An Australian Federal Police spokeswoman said in a statement that the boys, whose identities were not released, were “arrested under suspicion of attempting to prepare for incursions into foreign countries for the purpose of engaging in hostile activities”.

They were later handed back to their parents and an investigation is ongoing, she said.

Dutton would not say if the teens were linked to the Islamic State (ISIS) group. About 100 Australians were fighting with IS and other terrorist groups in Syria and Iraq, with another 150 supporting them at home, Prime Minister Tony Abbott said last week.

ISIS terrorism has recently been on the rise in Australia, with police several months ago arresting 15 terror suspects of an ISIS cell that was planning to behead a random member of the public in a campaign of terror.

Last month, local police foiled what they said was an “imminent” terror attack in Sydney by arresting two men and seizing a machete, a hunting knife, a video, and an ISIS flag.

Australia in September upgraded its terror threat to high amid growing concerns about militants returning from conflicts in the Middle East.

In December, Sydney was rocked by a siege at cafe by Iranian-born Man Haron Monis, a self-styled cleric with a history of extremist views.