The family of a missing 15-year-old girl who is feared to have travelled to Syria have made an appeal for her return.
Yusra Hussien, from Easton in Bristol, took an indirect flight to Turkey last week and is believed to be travelling with a 17-year-old girl from London.
Detectives said the priority was to find Yusra and "make sure she is safe".
Her family rejected claims she has become a "Jihadist bride", saying there was "no concrete evidence" of this.
Avon and Somerset Police said the investigation has been taken over by the South East Counter Terrorism Unit.
"They have strong international links which places them in the best position to pursue the investigation overseas and try to find Yusra and bring her home," a force spokesman said.
"We will continue to work closely with the family and the community in Bristol."
Yusra's mother, Safiya Hussien, said she loved and missed her daughter.
"We miss you so, so much. Please come home," she said.
The family appealed to the media not to speculate about what has happened to Yusra.
Aunt Sucdi Ali said her niece was a "typical teenager" and added they "were not here to talk about Isis" but to talk about Yusra.
She said: "The point here is there is a teenage girl who is missing."
Another aunt, Ikram Mohammed, said Yusra was "missed and was not in trouble" and said the family "was not angry and just wanted her back home".
The family said: "Yusra, our daughter is a very young, bright, bubbly girl who is loved by not only her family but her peers, teachers and her community.
"She loves to play table tennis and to ride her bicycle and she used to run with her brother, who's the next Mo Farah."
They said they were "very heartbroken" and said "every parent would relate to the pain" of not knowing if their child was safe.
Yusra was reported missing by her parents, who last saw her at about 07:00 BST on 24 September.
They said their daughter left for school as usual but was not there when her father went to pick her up at 15:30.
Police have been tracing the schoolgirl's movements from the moment she left her Easton home to her arrival in Istanbul.
Assistant Chief Constable Louisa Rolfe, from Avon and Somerset Police, said it was a "really sensitive investigation" and they were doing "everything nationally and internationally" to find Yusra.
She said: "We suspect she may have been influenced by others to leave the UK.
"It may have been online, it's possible that she's had contact with others directly before she left the UK, but there is no suggestion that this is directly linked with our community in Bristol.
"We don't have information to suggest she's gone to fight."
Ms Rolfe said police knew "exactly when and where" she had bought her ticket and "it wasn't at the airport".
She also said Yusra had "not taken a direct flight" to Istanbul but that she arrived in the Turkish city within 24 hours of leaving the UK.