Syrian rebels have made millions of dollars selling captured Islamic State (Isis) militants back to their counties of origin with some factions holding hundreds of the fighters hoping to cash in on the trade.

The Financial Times reported rebel groups, some of which have been armed by the US and the UK, have moved into areas of the wartime economy previously inhabited by human traffickers and smugglers and that as Isis has lost territory, its fighters have become highly prized commodities.

According to the FT, wanted individuals captured from Isis and sold to countries in the gulf through Turkey can fetch a minimum of $50,000 (£41,000). One rebel leader claimed to have been offered $10m (£8.2m) for handing over two Emirati jihadis with US passports.

The actual price eventually negotiated for the trade of the US militants was unclear with the rebel commander explaining they were eventually handed over for free. Other sources claimed a sum higher than $10m was secured.

Money can also be earned from Isis defectors who pay to be smuggled out of Isis territory and beyond. It can cost $10,000 (£8,200) for a fighter to leave Isis-controlled regions and a further $10,000 to enter Turkey.

As Isis loses control of the last of its territory in Iraq and is squeezed across Syria, rebels have said more than half of Isis' defectors have sought to travel to Idlib province to join groups linked to al-Qaeda.

rebels in Syria's al-Bab
Turkish military said they killed 44 Isis militants and wounded another 117 in Syrian border town of al-Bab as part of their Operation Euphrates Shield in which rebel fighters (in picture) are assisting the Turkish armed forces Reuters/Khalil Ashawi

The value of Isis fighters can in some cases be credibility or intelligence. The militants can be used as political leverage and even traded for rebel prisoners.

If a faction is seen to be holding an Isis fighter to gain crucial information from them, it can increase their standing in the eyes of foreign intelligence operatives. Around the Isis-held town of al-Bab, where rebels backed by Turkey troops and Russian airstrikes are fighting to dislodge the militants, prisoner exchanges have been taking place on a daily basis.