Three male teenagers were on Sunday being held in custody, British police said, after they were deported from Turkey from where they are believed to have been trying to travel to Syria.

The trio -- two aged 17 and from northwest London, the third aged 19 -- were being held on suspicion of preparing acts of terror,

Scotland Yard police headquarters in London said counter-terror officers were told Friday that the 17-year-olds had "gone missing and were believed to be travelling to Syria".

"Officers alerted the Turkish authorities who were able to intercept all three males, preventing travel to Syria," a spokesman said.

A Turkish official confirmed that the three were detained by security forces in Istanbul on Friday and were deported back to Britain on Saturday.

The 17-year-olds were detained upon information provided by Britain, the official told AFP.

Meanwhile the 19-year-old, identified as MAA, was detected by Turkish airport police who scrutinised the passengers arriving in Istanbul on a flight from Barcelona, the official said.

The official said that according to initial data, the teenagers were headed to Syria -- most probably to join the Islamic State group.

The Scotland Yard spokesman said the three had been returned to Britain and were arrested "on suspicion of the preparation of terrorist acts", contrary to the Terrorism Act 2006.

"All three have been taken to a central London police station, where they remain in custody."

The Turkish official praised the cooperation with the British authorities, saying: "This shows we can get results when serious co-operation, including timely intelligence, is in place."

It comes just weeks after an international police hunt was launched to find three east London schoolgirls who travelled to Istanbul on their journey to Syria.

However, Shamima Begum, 15, Amira Abase, also 15, and Kadiza Sultana, 16, are now feared to have reached the conflict zone.

An estimated 550 Western women have travelled to join extremists in Iraq and Syria -- while more than 500 people are believed to have left Britain to fight with IS, often travelling via neighbouring Turkey.

Keith Vaz, who chairs parliament's home affairs scrutiny committee, said Britain needed to prevent people travelling to Syria in the first place.

"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," he added.