Islamist groups have recruited dozens of former French soldiers, a troubling new report has revealed less than three months after a terrorist attack by a staff member at police headquarters in Paris shocked the nation.

More than a third of the ex-servicemen are converts to Islam and nearly half served in elite Foreign Legion, parachute, commando or marine units where they acquired expertise in combat and handling weapons and explosives.

The conservative newspaper Le Figaro published excerpts on Wednesday from the forthcoming report by the Centre for the Analysis of Terrorism, a Paris-based think tank.

The report says the French army “constitutes a strategic recruitment target for terrorist groups… and former soldiers represent tremendous assets for these groups.”

The report, “Soldiers and Jihad”, profiles 23 ex-servicemen “identified within terrorist organisations [mainly Isil] or implicated in plotting terrorist attacks”.

An earlier parliamentary report noted that about 30 former servicemen have joined jihadist groups since 2012. Several former Legionnaires have been arrested over terrorist plots in France, and ex-paratroopers or commandos have become leaders of Isil combat units in Syria or Iraq.