British police charged terror suspect at Heathrow, as Turkey deports IS militants to Europe

London's Metropolitan Police identified the man as Mamun Rashid, from east London, who had returned to the UK on Thursday as one of the dozens of suspected foreign Islamic State group militants deported by Turkey last week.

Turkey had confirmed it had deported an IS suspect to the UK.

In a statement, the Met said: "A man has been charged with a terrorism offence following an investigation by the Met's counter terrorism command," adding he would appear at Westminster magistrates court on Monday.

On Thursday, the police had said the man's arrest was "Syria-related", but did not give details. 

Turkey began a controversial push to expel foreign IS fighters in custody earlier this month, even if they had already been stripped of their citizenship by their country of origin.

One of the first to be deported, a US national, was trapped for days between the Turkish and Greek borders, eventually being sent back to the United States on Friday.

Eleven French fighters and seven Germans have also been sent back.

Earlier this week, the Turkish interior minister stated that Ankara had almost 1,200 foreign members of IS in custody, 287 of whom had been captured during its recent operation in northeastern Syria.

The UK and Belgium have reiterated their desire not to repatriate suspected IS members.

High-profile cases such as teen IS recruit Shamima Begum and Jack Letts have sparked court proceedings and fierce political debate.

It is unclear how Turkey will be able to repatriate IS members who have been made stateless. It is also unclear how Ankara will be able to successfully repatriate militants to countries such as the United Kingdom which have proven highly reluctant to take back suspected IS members.

Although the 1961 New York Convention made it illegal to leave people stateless, several countries, including the UK and France, have not ratified it, and recent cases have triggered prolonged legal battles. 

The UK alone has stripped more than 100 people of their citizenship for allegedly joining extremist groups abroad.

Both France and the UK have insisted that suspected members of the group be held responsible for their alleged crimes in the countries where they were committed, Iraq and Syria.

Human rights groups have, however, issued warnings over alleged torture and lack of due process in both countries. Baghdad has also sentenced IS members to death, a practise that is outlawed by London and Paris.

Agencies contributed to this report.