The Islamic State (ISIS) terrorist group has executed 100 of its own foreign fighters who tried to flee their headquarters in the Syrian city of Raqqa, AFP reported Saturday, citing the Financial Times (FT) newspaper.

An activist opposed to both ISIS and the regime of Syrian President Bashar Al-Assad, who is well-known to the British business broadsheet, said he had “verified 100 executions” of foreign ISIS fighters trying to leave the jihadist group’s de facto capital.

ISIS fighters in Raqqa said the group has created a military police to clamp down on foreign fighters who do not report for duty. Dozens of homes have been raided and many jihadists have been arrested, the FT reported.

ISIS has been accused of torturing and murdering prisoners, among them children and teenagers, and forcing Druze men to convert to Islam or die.

In one case, members of the group beheaded a person they said was a member of an Iraqi Shiite militia fighting for Assad, only to discover they had accidentally beheaded a fighter belonging to an allied rebel group.

In March, the group live-tweeted the amputation of a hand of a man charged with theft in the northern province of Aleppo.

The group, which has set up a “police force” in areas of Syria it controls, recently executed two men who were convicted of collaborating with the Assad regime.

The two men were brought to the village square, where dignitaries and local residents gathered. They fell to their knees, blindfolded and with their hands tied, before being beheaded.