Three male teens from Britain who reached Turkey before being deported to the U.K. and arrested are believed to be the latest examples of a worrying trend — the rising number of young Britons seeking to travel to Syria to join extremists there.

The three suspects were being questioned at a central London police station after their alleged bid to get to Syria, coming soon after three British schoolgirls managed to elude authorities and get to Syria last month. The girls are believed by police to have joined Islamic State in Iraq and Syria (ISIS) militants in their self-declared caliphate in parts of Syria and Iraq.

British police said the three males, two 17-year-old boys and a 19-year-old man, have been arrested on suspicion of planning terrorist acts. They haven't been charged and their names haven't been released.

When the schoolgirls managed to slip into Syria despite a search by both Turkish and British authorities, there was finger-pointing on both sides. Things were quite different Sunday, as Turkey and Britain hailed the fruits of their co-operation.

The male trio left Britain several days ago, travelling to Spain and then flying from Barcelona to Turkey. They were detained in Istanbul Friday after British officials notified Turkish authorities.

British legislator Keith Vaz, chairman of the Home Affairs Select Committee, said the case shows that the number of young Britons trying to reach the conflict zone in Syria "is on a much larger scale" than had been thought.

Vaz praised Turkish authorities for acting quickly to prevent the teens from entering Syria.

Police counterterrorism officials and security services personnel have said their resources have been badly stretched as they try to maintain surveillance on the growing number of individuals interested in joining the extremists. They have warned that some who return after spending time in the conflict zone plan to launch attacks inside Britain.

A senior Turkish government official, who can't be named because of Turkish rules that bar civil servants from speaking to journalists without prior authorization, said the two 17-year-old boys had been detained at Istanbul's Sabiha Gokcen airport Friday by Turkish authorities who were acting on intelligence provided by British officials.

Turkey seen as convenient entry point into Syria

The teenagers were planning to travel to Syria, the official said. Turkish authorities believe they wanted to join ISIS extremists, but the official cautioned that they weren't "100 per cent" certain that was their aim.

Britain Syria Missing Girls

Kadiza Sultana, 16, left, Shamima Begum, 15, centre and and Amira Abase, 15, right, left England in a suspected bid to travel to Syria to join the ISIS extremist group. (Metropolitan Police/Associated Press)

The 19-year-old man was detained at the airport after questioning by police based on profiling at the airport, the official said. British police originally believed only two teens were travelling, but soon learned that a third was involved.

They were deported to London on Saturday — instead of Spain as is the normal procedure in Turkey — because Britain insisted that they be returned to Britain, the Turkish official said.

The Turkish official described the incident as a "`joint Turkish-British operation," and said Turkey welcomed the timely intelligence provided by Britain.

"Turkey is doing all that it can to stop the passage into Syria, but there has to be co-operation," the official said. "This operation shows what can be achieved when there is co-operation."

Turkey's strategic position as a convenient link between Western Europe and Syria has meant that an increasing number of Britons have travelled there to use it as a jumping off point to enter Syria and link up with ISIS.

British police say roughly 700 Britons have travelled to Syria to join extremists. Recent cases indicate a growing number of young women are travelling there to become "jihadi brides."

Authorities say internet-based social media have made it much easier for young Britons to communicate with extremists inside Syria and that many are also drawn by websites touting the attraction of living under Islamic law.

With files from Nil Koksal