The activist, who spoke on condition of anonymity, told the newspaper he had "verified 100 executions" of foreign IS militants.
The Islamic State has reportedly created a police force tasked with keeping track of foreign fighters, who are now compelled to carry an ID. Those, who failed to report for duty, were allegedly arrested, the Financial Times said, citing activists.
The Islamic State has used adventurism as an efficient means to attract foreign recruits, political analyst Abdullah Hamidaddin argued. He recalled one of IS recruitment videos, saying it "is clearly not a call to jihad. This is a call to adventure and adventure in the minds of many youth is in risk and destruction."
Hence, numerous foreign fighters are trying to return home but fear they will be arrested. Up to 50 British nationals, disillusioned with fighting in Syria, want to return to the UK, AFP reports, citing researchers at the International Centre for the Study of Radicalization at King's College London.