US Intelligence estimates that more than 20,000 foreigners from 90 different countries are in Syria to fight alongside the Jihadists, according to the National Counter Terrorism Centre (NCTC). The estimation of foreign fighters in Syria is slightly higher than the one already in existence which estimated foreigners at 19,000.

The rate of arrivals in Syria is extremely high compared to other warzones such as Afghanistan, Pakistan, Iraq, Yemen or Somalia. The US estimates that at least 3.4 thousand foreign fighters come from western countries, out of which 150 are US citizens.

The number of would-be fighters traveling to the area is still rising, while intelligence suggests that the majority of said fighters will be swallowed up and integrated by ISIS in Syria and Iraq.