Turkey has hit back at Britain for suggesting its national airline could have done more to stop three schoolgirls travelling to Istanbul on their way "to join Isis" in Syria.
After David Cameron called for more action from internet companies and airlines in general, the Turkish government said it was "condemnable" that UK authorities had let the girls leave in the first place.
And Turkey's deputy prime minister Bulent Arinc said it would be "the British" to blame if the girls are not found, saying his government was only warned about them "three days later".
Kadiza Sultana, 16, Shamima Begum and Amira Abase, both 15, lied to their parents and boarded a flight from Gatwick to Istanbul last Tuesday, with at least one travelling on the passport of an older sibling.
Yesterday Mr Cameron told MPs he was "horrified" by the case, involving the three "straight A students" from Bethnal Green Academy school in east London.
Officers from the Metropolitan Police are now in Istanbul and "working closely with the Turkish authorities", though the nature of their role has not been confirmed.
Anti-Isis demonstrations across Europe
Anti-Isis demonstrations across Europe
1/10 Anti-Isis protests in Ankara, Turkey
A person holds a flag as police uses tear gas and water cannon in Ankara against demonstrators who protest against attacks launched by Islamic State insurgents targeting the Syrian city of Kobani and lack of action by the government
2/10 Anti-Isis protests in Diyarbaki, Turkey
Protesters clashing with riot police during a demonstration against Isis in Diyarbakir, southeast of Turkey
3/10 Anti-Isis protests in Diyarbaki, Turkey
Kurdish protesters in the southeastern city of Diyarbakir
4/10 Anti-Isis protests in Diyarbaki, Turkey
Kurdish protesters clash with Turkish riot policemen in the city of Diyarbakir
5/10 Anti-Isis protests in Brussels, Belgium
Riot police block Kurdish protesters as they gather in front of the entrance of the European Parliament in Brussels
6/10 Anti-Isis protests in Berlin, Germany
Demonstrators, including one holding a sign that reads: "Save the Kurds of Kobane from IS," and many of them members of Berlin's large Kurdish community, march to protest against the ongoing violence by militias of the Isis in Iraq and Syria in Berlin
7/10 Anti-Isis protests in Hamburg, Germany
Kurds protest against Isis militants advancing through the Syrian border city of Kobani, in Hamburg, Germany
8/10 Anti-Isis protests in London, UK
Kurdish protesters gather at Heathrow Airport as anti-Isis demonstrations take place across Europe
9/10 Anti-Isis protests in Paris, France
Kurds living in France demonstrate in Paris
10/10 Anti-Isis protests in Marseille, France
Kurdish people hold flag in Marseille during a protest against the threat of a "Syrian Kurdish population's genocide" by Isis militants and to support the population of the Syrian Kurdish town of Ain al-Arab, known as Kobani
But speaking to reporters on Tuesday morning, Turkey's 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."
Mr Cameron said that young people leaving to join Isis was "not just an issue for our police and border controls".
"What this incident has highlighted is the concerning situation where unaccompanied teenagers like these - who are not a known risk - can board a flight to Turkey without necessarily being asked questions by the airline,” he added.
"We need new proportionate arrangements with airlines to ensure that these at risk children are properly identified and questioned - and the Home Secretary and Transport Secretary will be working with the airlines to bring this about." Gatwick and Heathrow airport are among the airports that have already indicated that they are prepared to help.
Earlier, the girls' headteacher said he was "shocked and saddened" by the girls' disappearance, but said police had not found evidence that they were radicalised at school.
Mark Keary, principal of Bethnal Green Academy in east London, said police spoke to the girls after another student disappeared in December and indicated at the time that there was no evidence that they were at risk of being radicalised or absconding.
He also said access to social media at the school was "strictly regulated". A tweet sent from a Twitter account under Shamima's name was sent to Aqsa Mahmood, who left Glasgow for Syria to be a "jihadi bride" in 2013.
Additional reporting by PAReuse content