Three young British men who were stopped from travelling to Syria from Turkey and arrested have been released on bail, the Metropolitan Police says.
The three teenagers, two aged 17 and one 19, from north-west London were flown back to the UK on Saturday night.
They were arrested on suspicion of preparing terrorist acts and have been bailed pending further inquiries.
UK police alerted Turkish officials after a tip-off from the younger teenagers’ parents the Times has said.
Scotland Yard said counter-terrorism officers were initially made aware that the two 17-year-olds had gone missing and were believed to be travelling to Syria on Friday.
The parents of the pair contacted police when they did not return home after Friday prayers, according to the Times.
Further enquiries revealed they had travelled with a third man, UK police said.
“Officers alerted the Turkish authorities who were able to intercept all three males, preventing travel to Syria,” a police spokesman added.
They were returned to the UK at about 23:10 GMT on Saturday and were arrested by counter-terrorism officers.
They have been bailed to return to a central London police station pending further enquiries.
The trio had flown to Istanbul from Barcelona, in Spain, a Turkish official told the BBC.
The two 17-year-olds were stopped at Istanbul’s Sabiha Gokcen airport by Turkish authorities acting on intelligence provided by British police about the pair.
However, the 19-year-old man was only detained after being questioned by Turkish police, the official said. He was also arrested at the airport.
“This is a good and a clear example of how the security cooperation between Western intelligence agencies and Turkey should work,” the official added.
BBC correspondent Andy Moore said the development came after “recriminations” between UK police and Turkish officials following the disappearance of three London schoolgirls.
A senior Turkish government official told the BBC that Turkish security agencies have drawn up a “no-entry” list of 12,500 people, with some volunteers being as young as 14.
Largely using intelligence from Western agencies, they have also deported more than 1,100 people suspected of wanting to join Islamic State.
Reiterating Turkey’s willingness to stop the flow of foreign fighters into Syria, the official said that he has concerns about the failure in intelligence-sharing between Western security agencies and Turkey.
Speaking on the condition of anonymity, he complained that Western intelligence agencies are not doing enough to prevent the would-be fighters leaving their countries of origin.
He said that the flow of foreign fighters is been aided by a large human smuggling network, having one foot in Syria and the other in Western Europe.
The news comes as the National Police Counter Terrorism Network and partners have rolled out an advertising campaign designed to reach out to families, to prevent young people travelling to Syria.
It will involve adverts appearing in minority ethnic media across the country.
The awareness campaign features the relationship between a mother and daughter and encourages parents to discuss issues such as travelling to Syria and what they are viewing online.
In the last year 22 women and girls have been reported missing by families who feared they had travelled to Syria.
Deputy Assistant Commissioner Helen Ball, counter-terrorism co-ordinator, said police are increasingly concerned about the numbers of young women who have travelled or are intending to travel to Syria.
She said: “It is an extremely dangerous place and the reality of the lifestyle they are greeted with when they arrive is far from that promoted online by terrorist groups.
“The option of returning home is often taken away from them, leaving families at home devastated and with very few options to secure a safe return for their loved one.
“We want to increase families their confidence in the police and partners to encourage them to come forward at the earliest opportunity so that we can intervene and help.”
Kalsoom Bashir from the organisation Inspire, which works with Muslim women to tackle extremism said: “Having seen the devastation facing families where a loved one has travelled to Syria, I would advise families to keep their children close, to constantly remind them that they are loved, that they are part of a strong family network and that they can talk to you about anything they are worried about.”
Shamima Begum, Amira Abase, both 15, and Kadiza Sultana, 16 – all from London – took flights to Istanbul last month, from where it is feared they travelled to join Islamic State (IS) militants in Syria.
Their disappearance led to criticisms from Turkey’s deputy prime minister, who said Turkish officials had not been given enough warning about their disappearance.
“On this occasion it seems that the warning was raised in the UK and that was communicated very quickly to Turkey,” said our correspondent.
The Home Office says there are about 600 Britons “of interest” in Syria.
The BBC understands about 100 Western volunteers – including some Britons – are fighting as part of the 30,000-strong Kurdish forces against IS, while more than 500 Britons are believed to have travelled to join IS militants.