Child brides 'assault on values': Morrison

Authorities have intercepted a 14-year-old girl destined for an arranged wedding in Lebanon.

Customs and federal police stopped the teenager and her uncle at Sydney Airport on Friday after they learned she was being taken overseas to be married.

Authorities had been monitoring the case for some time and red flags were raised when the flights were booked.

Immigration Minister Scott Morrison says forced marriages are an "assault on Australian values".

"Where children are involved (arranged marriage) is an abomination," Mr Morrison said.

"I can confirm that an adult male and a female minor were prevented from boarding a flight at Sydney International Airport.

"The prevention from boarding was not counter-terror related."

Australian Federal Police are investigating the case.

"AFP is making further inquiries in relation to this matter and it is not appropriate to comment further," a spokeswoman said.

Authorities have been on high alert for cases of arranged marriages in the wake of an Islamic State social media campaign to recruit young brides to wed terrorists.

There is no suggestion this incident was ISIL-related.

The young girl and her uncle were questioned before being allowed to leave the airport.