The ISIS extremist group “foreign fighters” returning home from the conflict in Iraq and Syria should be charged with war crimes, an EU-backed body said on Saturday.

Many such suspects currently only face charges under domestic terrorism laws, said the Genocide Network, a body set up in 2002 by the European Union to coordinate between national investigators and prosecutors.

But they could face wider charges under international laws covering some of the worst crimes that happen during conflict, including genocide and crimes against humanity, said the network which is based at Europe's judicial cooperation agency Eurojust.

“ISIS should not only be considered as a terrorist organization,” it said in a new report.

The extremist group could be treated under international humanitarian law as a “party to a non-international armed conflict in Iraq and Syria acting as an organized non-state armed group,” it said.

“Therefore, its members and foreign terrorist fighters could be responsible for committing war crimes and other core international crimes.”

Examples of returned foreign fighters being prosecuted under cumulative charges already exist in France, Germany and the Netherlands, the network report said.

For instance, a German extremist who recorded a video on a mobile phone of him cutting off the ears and nose of a dead Syrian soldier outside the Syrian city of Aleppo, was sentenced to eight-and-a-half years behind bars.

He was convicted of the war crime of the war crime of “outrage upon personal dignity.”

In the Netherlands, a Dutch extremist fighter was sentenced to seven-and-a-half years for posing laughing next to a man crucified on a cross and sharing the picture on Facebook.

Eurojust and the Genocide Network say that such prosecutions could also be established on a global scale to prosecute other foreign fighters returning to their countries of origin.

“Prosecuting terrorism offences combined with acts of core international crimes ensures the full criminal responsibility of perpetrators, results in higher sentences and delivers more justice for victims, the report said.

“By recognizing and naming these crimes for what they are, justice can hence be brought to victims,” it added.

The report quoted a study done by the London-based International Centre for the Study of Radicalization in mid-2018, saying there were 7,252 people in eastern Europe and 5,904 people in western Europe associated with the IS group including former fighters, women and children.

Some 2,000 fighters are still detained by Syrian forces and another 1,000 are in detention in Iraq, many of them European citizens mainly from France, Britain and Germany.