A French extremist went on trial Thursday (June 25th) on terror charges amid accusations that he oversaw executions in Syria as a senior figure in the "Islamic State of Iraq and Syria" (ISIS).

Tyler Vilus, 30, is facing charges of belonging to a terrorist group, heading a group of ISIS fighters and "aggravated murder" between 2013 and 2015. He faces a life sentence if convicted.

Investigators suspect him of being part of "Al-Muhajireen" (the immigrants) brigade, a squadron that tortured and carried out summary executions, which he denies.

Vilus is also accused of supervising executions as a member of the "religious police" in the north-eastern Syrian town al-Shaddadi, close to the Iraqi border.

In a 2015 video published by ISIS's media department, a man alleged to be Vilus is two metres away as two kneeling and blindfolded prisoners are executed with a bullet to the head.

One of the prisoners had fought with the Free Syrian Army (FSA) and the other was a Syrian regime soldier.

Vilus was arrested at an Istanbul airport with a Swiss passport in July 2015 and was subsequently deported to France.

His arrest and trial are being seen as a major coup for the French security services, as Vilus is believed to have known many French extremists in Syria.

Vilus has admitted to being in contact with the man French secret services believe is the mastermind of the November 2015 terror attacks in Paris, Abdelhamid Abaaoud.

Vilus' mother travelled three times to Syria in support of her son and was sentenced to 10 years in prison in June 2017 for her "unfailing commitment" to violent extremism.