Channel 4 News
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Between late 2011 to December 2013, the International Centre for the Study of Radicalisation (ICSR) estimate that up to 11,000 individuals from 74 countries joined the opposition fighters in Syria against the Assad regime. Though the vast majority are from Arab nations, there was a steep rise in the number of western fighters recorded by the ICSR, based in Kings College London, between April and December 2013 - tripling from 600 to 1,900. The total number of foreign fighters inside Syria and Iraq has now exceeded 20,000, according to ICSR.