The Bradford sisters missing with their nine children were stopped from leaving the UK in March, ITV News has learned.
Their trip to Saudi Arabia was rebooked for May but there is no suggestion they were intending to travel to Syria at that time. Police are now trying to work out when the trip was planned.
One of three missing sisters has contacted her family in Bradford with information suggesting they may have already crossed the border into Syria, police have said.
West Yorkshire Police said: "Contact has been made by one of the missing women and there is an indication that they may have already crossed the border into Syria but this is uncorroborated."
Assistant Chief Constable Russ Foster, from West Yorkshire Police, said: "We are extremely concerned for the safety of this family, especially the nine children aged between 3-15 years.
"The family have reached out to Khadija, Sugra and Zohra, in the hope that they hear their messages and we encourage them to make contact with us so we can return them and the children safely to their families who are extremely worried about them."
Speaking from Pakistan, one of the husbands of the missing Bradford thought to be heading to Syria has told ITV News of his worry.
Here's what we know about the Bradford family of 12 who are feared to be travelling to Syria.