Three sisters from England's Bradford city are believed to have travelled to Syria with their nine children during a pilgrimage to Saudi Arabia, media reported on Tuesday.
An urgent appeal has been launched to track them down, the Guardian reported.
The 12 members of the Dawood family from Bradford, West Yorkshire, are aged between three and 34 and were due to return last Thursday. They left for Saudi Arabia on May 28.
"There were serious concerns that they may be headed to Syria and it was possible they had travelled there via Turkey. I have been instructed by two of the fathers of the nine children, who had become extremely concerned when they could not get in touch with their families," said Balaal Khan, a solicitor.
"The fathers are concerned that their children's lives are in danger. The major concern is for the well-being of the children. The fathers are distraught; they feel helpless and they don't know what to do," Khan added.
Khan said he understood that the three sisters had a brother, who had already left Britain for Syria. However, there is no further information about him, he said.
Also Read
Preliminary inquiries suggest 10 members of the family boarded a flight from Medina, Saudi Arabia, to Istanbul, Turkey, on June 9.
Those missing after boarding the flight have been identified as Khadija Dawood, 30, and her children Maryam Siddiqui, seven, and Muhammad Haseeb, five; Sugra Dawood, 34, and her children Junaid Ahmed Iqbal, 15, Ibrahim Iqbal, 14, Zaynab Iqbal, eight, Mariya Iqbal, five, and Ismaeel Iqbal, three; and Zohra Dawood, 33.
However, no details could be found for Zohra Dawood's two children -- Haafiyah Binte Zubair, eight, and Nurah Binti Zubair, five -- boarding the flight to Istanbul.