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ISIS flagReuters

Three London schoolgirls who fled to Syria are believed to have stolen family jewelry to fund their travel, police said Tuesday, according to the AFP news agency.

The three, Kadiza Sultana, 16, and 15-year-olds Shamima Begum and Amira Abase, left their homes last month and flew to Istanbul, from where they are believed to have joined Islamic State (ISIS) jihadists in Syria.

Giving evidence before parliament's home affairs committee, Britain's national police lead on counter-terrorism, Mark Rowley, said the girls paid a travel agent more than £1,000 ($1,506) for their flights.

Asked where they found the money, he said, "We think it's linked to theft from families. We think it's linked to taking jewelry from one of their family members."

However, family members later said that the girls must have found additional funds elsewhere, as the jewelry that was missing was not of great value.

"We haven't lost £2000 worth of jewelry," Shamima's sister Renu Begum told ITV News.

"I feel there is someone out there helping in terms of funding because there's no way my sister has got the cash to fund herself," said Kadiza's sister Halima Khanom.

"I really hope the police would now make it their business to establish where these funds came from because it clearly wasn't from home," added Kadiza's cousin Fahmida Aziz.

The girls are among 26 British young women who have gone to join ISIS fighters in Syria, according to Rowley, who is assistant commissioner of London's Metropolitan Police.

But he said that so far "we have no evidence to suggest they are involved in terrorism", and they could return home to Britain without facing charges.

Earlier this week it was reported that the three girls crossed into Syria via Turkey and are believed to be staying at a house in the city of Raqqa, a stronghold of ISIS.

Last week, CCTV footage emerged which appeared to show the three teenagers at a bus station in Istanbul.

In the footage, the girls were seen wrapped in heavy winter jackets, two with hoods pulled up, and carrying packed sports bags and holdalls.

The footage was recorded in the early hours of February 18, less than 24 hours after the trio left their London homes, telling their families they would be out for the day.

Turkey, which has been accused by its Western allies of failing to do enough to stop jihadists crossing into Syria from its territory, has accused Britain of failing to provide information about the girls sooner.