One hundred foreign fighters who joined the Islamic State group were killed for attempting to flee the extremist group’s headquarters in the Syrian city of Raqqa, the Financial Times reported Friday. Some jihadists who were drawn to Syria have now become disenchanted with the grueling fight, but the leaders of the militant group formerly known as either ISIS or ISIL won’t let them return home, Agence France-Presse reported.

In October, 12 foreign fighters from various European countries wanted to return to their homes, but said they were being held prisoner by the Islamic State. The jihadists complained they were fighting against other rebel groups in Syria rather than against the regime of President Bashar Assad. A British foreign fighter contacted researchers at the International Center for the Study of Radicalization at King’s College London, saying between 30 and 50 British foreign fighters wished to return home, but feared they would face prosecution, according to AFP.

The Islamic State has reportedly created a military police force to penalize those who do not report for duty. The ISIS police have arrested 400 fighters in Raqqa for not reporting to its offices within 48 hours of receiving new regulations purportedly promulgated by the group. The regulations require Islamic militants to now carry documentation proving they are fighters and identifying their assigned missions, the Financial Times reported.

One foreign fighter quoted by the Financial Times said fighters are becoming increasingly unhappy with their leaders. “The situation is not good,” he told the U.K.-based newspaper. “We aren’t able to speak the truth, and we are forced to do useless things.” Residents in Raqqa have also noticed signs of discontent among Islamic State fighters in the northern city.

A young Syrian man who joined the militant group because he was moved by tribal allegiances told NPR News he fled to Turkey after realizing its brutal ideology. “ISIS wants to kill everyone who says, ‘No,’” the former fighter told NPR in September. “Everyone must be with them,” he said, adding that defectors like him are severely punished should they be caught. “[If] you turn against ISIS, they will kill you.”