Three teenagers who were stopped from travelling to Syria from Turkey have been flown back to the UK and arrested, Scotland Yard has said.

Two boys aged 17 from north-west London and a man aged 19 were returned to the UK on Saturday night, the Met said.

They were arrested on suspicion of preparing terrorist acts and have been released on bail.

They were reported as missing on Friday and were detained after UK police alerted Turkish officials, it added.

Scotland Yard said counter-terrorism officers had initially been made aware that the two 17-year-old boys had gone missing and were believed to be travelling to Syria.

Further enquiries revealed they had travelled with a third man, UK police added.

"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.

'SECURITY CO-OPERATION'

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 questioning 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.

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 officials in the country 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," our correspondent said.

The BBC's Selin Girit, in Instanbul, said the deportation of the two 17-year-old boys and 19-year-old man shows that when Turkish police have information "they can co-operate".

"When the three UK schoolgirls went missing Turkish officials said 'it is not us to blame because we were not passed the information of these missing girls. How can we find and locate and deport them when we do not have the necessary information?'," she said.

"But this shows when there is a co-operation between intelligence services, between police, Turkish police can act accordingly."

'BELOVED DAUGHTERS'

Meanwhile, the families of the missing schoolgirls have called for the "immediate safe return of our beloved daughters".

In a joint statement, the families repeated criticism of how the police and local authorities handled the cases.

They said that "had we been made aware of circumstances sooner, we ourselves could have taken measures to stop the girls from leaving the UK".

Mohammed Akunjee, a lawyer representing the families, said he hoped the authorities had learnt lessons and would apply them to future cases.

"As I understand it, the UK government has no actual policy with respect to arresting and charging a given individual. Each case, as we understand it, is treated on a case-by-case basis," he said.

On Saturday, a fourth missing schoolgirl - who was a friend of the three London schoolgirls - was named as Sharmeena Begum.

The 15-year-old, from Bethnal Green, is thought to have left the UK ahead of her friends in December to join IS militants.

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.

Labour MP Keith Vaz, chairman of the Home Affairs Select Committee, welcomed the action taken by the Turkish authorities, adding: "We need to be vigilant. Clearly this flight of young people to Turkey in order to go to Syria is on a much larger scale than we envisaged."