Authorities fear that twin runaway British girls fled to Syria to join a terrorist group, possibly the Islamic State of Iraq and Syria or other jihadist groups that have called on British Muslims to join their ranks.

The 16-year-olds, originally believed to be from Somalia, reportedly snuck out of their rooms June 26 and flew from Manchester Airport to Istanbul, the Manchester Evening News reported Sunday. Their family said the girls later spoke to them from Syria.

The girls may have tried to join their brother, who is a fighter for the Islamic State.

"Since their departure, the girls have been in contact with their family,” Greater Manchester Police said in a statement, the BBC reported. "We are attempting to confirm their current location and secure the well-being of both girls."

Sources told the Daily Mail the girls most likely headed to Syria to be "jihad brides," not to fight for the Islamic State.

“We’ve seized their computers and not found any videos or statements of intent, but are not ruling anything out,” a source told the British tabloid.

Sir Peter Fahy, chief constable for the Greater Manchester Police, said there are local youth who are being “brainwashed” by “perverted messages” from terror groups. Fahy also sits on the Association of Chief Police Officers’ counterterrorism committee.

“We’ve got some information about girls trying to get to Syria and some we believe may have gone out there on the idea of being a jihad bride. So there are a number of absolutely perverted messages which can brainwash impressionable young people, and parents are feeling desperate about this,” he said. “It’s a bit like parents agonizing about youngsters getting into street gangs or drugs, but the consequences are far more extreme.”

According to the BBC, 500 Muslims from the U.K. are believed to have traveled to Syria to join terror groups.