Three teenage girls from London feared to have run off to join the Islamic State (IS) group are believed to have crossed from Turkey into Syria, British police said Tuesday.
Close friends Kadiza Sultana, 16, and 15-year-olds Shamima Begum and Amira Abase, boarded a flight from London Gatwick to Istanbul last Tuesday. Their families launched a public appeal for them to return home.
London's Scotland Yard said counter-terrorism detectives leading the search for the teenagers "now have reason to believe that they are no longer in Turkey and have crossed into Syria".
In a statement it added: "Officers continue to work closely with the Turkish authorities on this investigation."
Citing unnamed sources inside Syria, the BBC reported that the girls had been smuggled into Syria from Turkey four or five days ago near the Kilis border crossing.
Turkey, which has been accused by its Western allies of failing to do enough to stop jihadists crossing into Syria from its territory, had earlier accused Britain of failing to provide information about the girls sooner.
"It is a reprehensible act for Britain, a country famous for its Scotland Yard, to let the three girls... leave Heathrow airport (sic) for Istanbul and then let us know three days later," Deputy Prime Minister and government spokesman Bulent Arinc told Turkish reporters late Monday.
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"Turkey cannot be held responsible for what happened," he added. "We don't have a mechanism in place that allows us to question the intentions of tourists and read their minds."
Scotland Yard said it had informed the Turkish embassy in London the day after the girls disappeared and said the Turkish authorities had since provided "great assistance".
But Arinc said Britain had failed to take the "necessary measures" and that it "should have informed us and shared intelligence with us".
Arinc's complaints echo similar remarks made by Turkish officials after Hayat Boumeddiene, the wanted partner of one of the gunmen behind the January terror attacks in France, travelled undetected through Turkey on her way to Syria.
In that case, Ankara accused the French authorities of failing to share information in a timely manner about the wanted woman's departure for Turkey.
British anti-terror police made an unprecedented appeal on Friday to find the three girls, two of whom are British and the third a German citizen.
Richard Walton, head of the police's Counter Terrorism Command, said he was "extremely concerned" for the wellbeing of the girls, who were all studying at Bethnal Green Academy in east London.
An estimated 550 Western women have travelled to join the militants in Iraq and Syria.