The battle for Mosul has seen the "Islamic State of Iraq and the Levant" (ISIL) increasingly resort to weaponised drones, AFP reported Tuesday (November 29th).

France issued an internal note to its security forces last week warning that "this threat is to be taken into account nationwide" and ordering any drone be treated as a "suspicious package".

The first record of a deadly ISIL drone attack was in October when two Iraqi Kurdish fighters were killed and two French special forces soldiers wounded.

"The use of drones by terrorist and insurgent forces is a growing issue of international concern," Conflict Armament Research executive director James Bevan wrote in a recent report.

"It is a threat we are looking into, especially with all those who will return from Iraq and Syria with bags of battle experience," a French official told AFP.

Extremist fighters have used drones for some time for reconnaissance missions, but they have more recently tried to modify them.

Experts argue that, compared to the suicide car and truck bombs ISIL uses, drones represent a minor threat. Yet there is evidence that ISIL has been trying to modify its drones.

"No terrorist entity to date has demonstrated UAS (unmanned aircraft systems) capability that would be considered highly capable, highly lethal and highly secure," Don Rassler, from the Combating Terrorism Centre, said in an October report. He warned that could change soon, however.

To counter this new threat, some countries have started developing defence systems capable of spotting, tracking and destroying drones.