Prime Minister David Cameron said young people travelling to join Islamic State are "deeply misguided" after a fresh wave of arrests over Syria-related terror offences.
An 18-year-old remained in custody tonight on suspicion of preparing to travel to Syria to join militant group Islamic State after a raid by counter-terrorism officers in the Hodge Hill area of Birmingham early this morning, West Midlands Police said.
The swoop followed the arrest of a 19-year-old man and two 17-year-old boys from north-west London on Saturday, on suspicion of preparing terrorist acts.
The three, all from Brent in north west London, were stopped by officials in Turkey as they tried to travel to Syria, and returned to the UK over the weekend. All three have been bailed while investigations continue.
Speaking to BuzzFeed this evening about the Londoners, Mr Cameron said it was right the teenage boys had been arrested and questioned on their return and that he now wanted to see three girls who fled Bethnal Green in east London for Syria brought back as well.
He said: "I think they are deeply misguided and they are potentially going to join a criminal organisation which could make them part of a criminal or terrorist conspiracy. We want to get them back and try to get this radical nonsense out of their heads.
"That people in an outstanding school can opt to go and join a death cult in Syria that believes in throwing gay people off buildings and cutting people's heads off in the desert is deeply depressing and we should be really worried about this as a country."
The families of two of the three London teenagers arrested reportedly raised the alarm to police, leading to the three being detained by the Turkish authorities.
On Friday police were made aware the two younger boys had gone missing and were believed to be travelling to Syria.
Inquiries revealed they had travelled with a third person, the 19-year-old man.
The families of the younger boys alerted officers when the pair did not return from Friday prayers, according to reports.
The three are reported to have travelled to Spain before taking a flight to Turkey - a route taken by Hayat Boumedienne, the widow of one of the terrorists who carried out the Charlie Hebdo attack in Paris in January - though the Foreign Office could not confirm this.
Brent Council leader Muhammed Butt welcomed the quick actions of the men's families, saying that their decision to call authorities was "vital" in getting the youngsters home safely.
He said: "It is good to know that these young men are now safely home with their families. This is because the families involved decided to call the authorities as soon as they realised their children were missing."
It comes just weeks after an international manhunt was launched to find the three London schoolgirls who travelled to Istanbul on their journey to Syria.
However, Shamima Begum, 15, Amira Abase, also 15, and Kadiza Sultana, 16, who are pupils at Bethnal Green Academy, are now feared to have reached the conflict zone to become so-called "jihadi brides" with Islamic State.
Their families appealed for them to come home immediately, saying they felt their loss "more acutely" on Mother's Day.
About 600 Britons are believed to have travelled to Syria and Iraq since the conflict began.
Sajda Mughal, director of the JAN Trust which offers workshops to Muslim parents on the dangers of online radicalisation, said: "Whilst these cases are coming out in the media and people become aware, this is not enough to tackle the issue of radicalisation.
"What is required is that Muslim homes across the UK must be educated on the issue and online radicalisation to take ownership and so that they can safeguard their children."