Three missing teenagers believed to be heading to join Islamic State militants are thought to have crossed into Syria, UK police say.
The London schoolgirls were smuggled into Syria from Turkey four or five days ago, the BBC understands.
Sources said the girls had entered Syria near the Kilis border crossing.
Bethnal Green Academy pupils Shamima Begum and Amira Abase, both 15, and Kadiza Sultana, 16, travelled to Istanbul on 17 February.
They flew from Gatwick to Turkey after telling their parents they were going out for the day.
The Metropolitan Police said it "now had reason to believe that they are no longer in Turkey and have crossed into Syria".
"Officers continue to work closely with the Turkish authorities on this investigation," the force said in a statement.
It comes after the girls' families made a number of emotional appeals for them to return.
'Condemnable act' Earlier, Scotland Yard denied it had taken three days to inform officials in Turkey about the schoolgirls travelling to Syria.
Turkey's Deputy Prime Minister Bulent Arinc said officials would have taken "necessary measures" had they known earlier.
But Scotland Yard has said it began working with Turkish authorities a day after the girls went missing.
Mr Arinc said: "It is a condemnable act for Britain to let three girls... come to Istanbul and then let us know three days later.
"They haven't taken the necessary measures. The search is ongoing.
"It would be great if we can find them. But if we can't, it is not us who will be responsible, but the British."
The three girls had been studying for their GCSEs at the school in Tower Hamlets, east London - from where a fourth pupil is believed to have travelled to Syria in December.