An official says two Australian brothers aged 16 and 17 have been stopped at Sydney Airport on suspicion they were headed to the Middle East to fight with the Islamic State group.

Border Protection Minister Peter Dutton told reporters Sunday the young brothers from Sydney raised the suspicions of customs officials as they attempted to depart Sydney on Friday.

Dutton would not detail where the pair were headed apart from a Middle Eastern "conflict zone."

He also refused to say what was found in the boys' luggage that raised officials' suspicions and led to the brothers beings reported to the airport's new counterterrorism unit.

He says the boys' parents were "as shocked as any of us would be" to discover their sons had attempted to leave the country.