New York-based intelligence firm, the Soufan Group, estimated in June that at least 12,000 terrorists from 81 countries, including some 3,000 European nationals, are fighting in Syria.
The number is said to be unprecedented in the history of armed conflicts in the modern age.
Other media accounts estimate that higher numbers of foreign mercenaries are involved in the Syrian war, including over 2000 Europeans and 100 Americans.
The ISIL Takfiri terrorist group has translated its recruitment videos into myriads of languages, including Urdu, Tamil, and Bahasa Indonesia.
Although the majority of foreign terrorists fighting inside Syria are still from Arab countries, European governments have become deeply concerned about the threat of extremism in their countries when those radicalized terrorists return home.
On Wednesday, German Chancellor Angela Merkel warned that at least 400 German citizens are fighting alongside the ISIL militants in Syria and Iraq.
The United Nations warned on Thursday that the violence by ISIL Takfiri terrorists against Syrian civilians has reached “a new level.”
Takfiri terrorists have been committing horrific crimes against innocent civilians since the outbreak of the crisis in Syria in March 2011.
ISIL terrorists have been behind many of the deadly bomb attacks targeting both civilians and government institutions across Syria over the past three years. They have also mass executed hundreds of people in Iraq and Syria.
The foreign-backed ISIL violence has spilled over to neighboring Iraq.
The terrorist group has links with Saudi intelligence and is believed to be supported by the Israeli regime.