A second Frenchman who took part in the brutal beheading of aid worker Peter Kassig by Islamic State (ISIS) was identified on Wednesday, AFP reports.

The man appeared unmasked in the grisly execution video among other ISIS jihadists, many of whom are believed to be Western fighters.

Several European countries are probing the possible involvement of their nationals in the execution of 18 Syrian prisoners and Kassig.

The video sparked global horror after its release on Sunday by ISIS.

One foreigner, 22-year-old Maxime Hauchard from Normandy in northern France, was quickly identified by French prosecutors.

A source close to the French investigation on Wednesday identified a second national as 22-year-old Mickael Dos Santos from an eastern Paris suburb, who goes by the name of Abu Othman.

He is believed to have left for Syria in the autumn of last year, and became known to investigators shortly afterwards during a probe into a network channeling jihadists into the war-torn country.

“The man concerned is known for his terrorist involvement in Syria and his violent behavior shown on social networks,” Prime Minister Manuel Valls said, without confirming his identity.

Over 1,000 French citizens have reportedly left to join ISIS. They are a part of a group of more than 15,000 foreign nationals who have crossed the borders into Syria and Iraq to join the ranks of ISIS.

In addition to France, the recruits are coming from, among others, Russia, the United Kingdom and Ireland.