One has been named as Shamima Begum, 15, who may be traveling under the name of 17-year-old Aklima Begum, and a second as Kadiza Sultana, 16. The third girl has not been named at the request of her family, police said.

Richard Walton, of Counter Terrorism Command, said: “We are extremely concerned for the safety of these young girls and would urge anyone with information to come forward and speak to police. Our priority is the safe return of these girls to their families.

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She was given a four-year prison sentence last month after admitting wanting to become an ISIS bride and participate in its jihad in the Mideast.

CNN’s Laura Perez Maestro contributed to this report.