Two British Muslim fathers whose wives and children are suspected to have traveled to join jihadists in Syria made tearful appeals for them to return home on Tuesday.
The 12 family members, from Bradford in northern England, went missing after travelling to Medina in Saudi Arabia for an Islamic pilgrimage.
Sisters Sugra Dawood, 34, Zohra Dawood, 33, and Khadija Dawood, 30, traveled to Medina with their nine children, aged three to 15, on May 28.
"All of you, I can't live without you. Please, please come back home," said Akhtar Iqbal, husband of Sugra Dawood, at an emotional press conference in Bradford.
Mohammed Shoaib, husband of Khadija Dawood, said: "We had a perfect relationship, we had a lovely family. Please contact me whenever you want. Please come back."
Balaal Khan, a lawyer for the children's fathers, said the sisters were believed to have a relative fighting for either the Islamic State group (ISIS) or another extremist organisation in Syria, and it was feared they have gone to see him.
Khan said the fathers last spoke to their children on June 8, and appealed for anyone with any information about the missing women to come forward.
"They have been distraught, crying, they don't know what to do," he said of the fathers.
The women and children were due to return to Bradford last Thursday.
Preliminary inquiries suggest at least 10 family members boarded a flight from Medina to Istanbul – a commonly used route into Syria.
An eight-year-old and a five-year-old in the group are not believed to have boarded the same flight.
The counter-terrorism unit of the regional police force is leading the investigation.
"We are extremely concerned for the safety of the family and would urge anyone with information to come forward and speak to us," Russ Foster, an assistant chief police constable, said in a statement.
"There are lines of enquiry being progressed with the Turkish authorities and the possibility of the family attempting to travel to Syria is being explored," the statement said, adding however that the police were "keeping an open mind" about what might have happened.