Story highlights British teenager Kadiza Sultana believed to have died in Syrian airstrikes

Told family she wanted to leave Raqqa and was scared for safety

London (CNN) Relatives of one of three British schoolgirls who left the country last year apparently to join ISIS in Syria, fear she is dead, a family attorney said Thursday.

Kadiza Sultana, then 16, and two other teens boarded a flight from London's Gatwick Airport to Istanbul on February 17, 2015. They were thought to have crossed the border from Turkey into Syria within days.

Kadiza Sultana was 16 when she left the UK to join ISIS.

Tasnime Akunjee, an attorney who represents Sultana's family, said the family received news of her death in Raqqa "some weeks ago" -- at the same time communication from her stopped. Akunjee said he had been working with the family to try to bring Sultana back to London.

Reports of Sultana's death have not been independently confirmed.

The UK Foreign Office said: "It is extremely difficult to confirm the status and whereabouts of British nationals in Syria as all UK consular services there are suspended."

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