Attorney Tasnime Akunjee said the family of Kadiza Sultana learned of her death in Raqqa, Syria, a few weeks ago.
She was believed to have been killed by a Russian air strike in Raqqa, ITV News reported earlier on Thursday.
Sultana was making plans to return to Britain and her family was communicating with her to discuss her possible escape from Raqqa, according to an interview published by ITV with Sultana’s sister, which includes recordings of purported phone calls between the sisters.
Sultana, 16, along with two other friends, flew from London’s Gatwick Airport to Turkey on Feb. 17, 2015.
The British Home Office and British Interior Ministry could not be reached immediately for a comment.