Bedfordshire Police are investigating whether a Luton family of 12 has fled to Syria after failing to return from a trip to their native Bangladesh.
Three generations of the family -- aged between one and 75 -- could have travelled into the war-torn country where Isis controls vast swathes of land on May 17, police fear.
They are thought to have stopped in Turkey -- a known gateway for runaway Britons and those seeking to take up arms with the terrorist group -- before crossing the border into neighbouring Syria.
The family flew to Bangladesh on 10 April and before flying to Istanbul on 11 May.
Bedfordshire Police said a family member had been in touch with relatives in the UK but did not say where they were, the BBC reported.
There is no suggestion their journey is related to terrorism and police are continuing their enquiries.