Lawyers representing the family of three British sisters who disappeared in the Middle East with their nine children have slammed the police, arguing the authorities were complicit in the grooming and radicalization of the women.

The attorneys wrote to lawmaker Keith Vaz, alleging the police had been "encouraging contact with the brother-in-law of our client whom, it is believed, is fighting in Syria." The letter suggests "reckless disregard as to the consequences of any such contact on the families of those whom we represent."

Police declined immediate comment Sunday. They are trying to establish the whereabouts of the Dawood family, from Bradford in northern England, who failed to return from a Muslim pilgrimage to Saudi Arabia. They were due to return June 11, but broke off contact on June 9.