The Islamic State of Iraq and Syria (ISIS) has been known for funding its reign of terror in a number of ways, including human and human-organ trafficking.

Now, Syrian rebels have reportedly turned the tables on them and are reportedly making millions by selling them! What's more, most — if not all — of these Syrian rebels belong to factions that are backed by external forces, like the United States and Turkey.

Also read: The man-eating dogs of Syria: Canines develop taste for human flesh as ISIS discards corpses of people it executes

Who's buying?

A Financial Times report has said that Syrian rebels are funding their fight against the regime forces under President Bashar al-Assad by "selling back" captured ISIS militants to their home countries for a premium. While some have been "valued" at tens of thousands of dollars — already a steep price — by their home countries; in some cases, the price has reportedly gone up to millions.

The report quotes a man as saying, without divulging his real name: "Every faction trades in ISIS fighters. Don't believe anyone who says they don't." The captured ISIS militants are first taken to Turkey, which borders both Iraq and Syria, and then sold to their home countries.

Lucrative trade

Countries are only too happy to take back their own citizens, thereby reducing chances of allegations that they let their people fight for the ISIS. In one case, two individuals were reportedly sold back to the United Arab Emirates for a sum of $10 million, with some rebel factions claiming that the price negotiated for them was even higher than that.

Money is made from ISIS militants in other ways as well. Some defectors from the terrorist group have been known to pay thousands of dollars in exchange of being smuggled out of the ISIS-controlled territory for fear of being executed. There are reportedly separate costs for being taken out of regions controlled by the ISIS, and for being crossed over to Turkey — $10,000 for each leg.