Two Kurdish Peshmerga were killed and a pair of French commandos wounded after a booby-trapped drone launched by ISIL fighters blew up earlier this month near Iraq's Mosul city.
One of the French soldiers sustained life-threatening injuries and both were flown back to France for treatment. Other French troops were reportedly lightly wounded by the drone blast.
"It seems it was booby-trapped," Jabbar al-Yawar, secretary-general of the autonomous Kurdish region's defence ministry, told the Reuters news agency on Wednesday, adding that it detonated when soldiers attempted to pick it up.
French government spokesman Stephane Le Foll confirmed the injuries. "Yes. They were injured by a drone that landed and then exploded," he told reporters.
The use by ISIL of drones carrying explosives intended to blow up when they hit their target is a relatively new development.
Calling it a Trojan Horse-style attack, Air Force Colonel John Dorrian, spokesman for the US-led military coalition in Iraq, said an improvised device on the drone exploded after it was taken back to base.
A US official added it looked like a Styrofoam model plane that was taped together in a rudimentary style. The official - who spoke on condition of anonymity - said it appeared to be carrying a C-4 charge and batteries, and may have had a timer on it.
"They can just buy them as anybody else would," Dorian told reporters. "Some of those are available on Amazon."
Chris Woods - head of the Airwars project, which tracks the international air war in Iraq, Syria and Libya - said, "there are a million ways you can weaponise drones - fire rockets, strap things in and crash them".
"This is the stuff everyone has been terrified about for years, and now it's a reality," Woods added.
Yawar, speaking from Erbil, capital of the Kurdish region of northern Iraq, said the French soldiers had been training Kurdish fighters near the town of Dohuk.
Peshmerga forces plan to take part in a planned US-backed Iraqi military offensive to oust Islamic State of Iraq and the Levant (ISIL, also known as ISIS) from Mosul.
The US-led coalition against ISIL includes French, British, Canadian and other Western military contingents.
France has about 500 troops in Iraq as part of a US-led coalition. The numbers include special forces that have been training Kurdish Peshmerga fighters.
Mosul is Iraq's second largest city and the last urban centre still under ISIL control in Iraq after a series of government offensives to reverse the group's lightning-quick seizure of territory in 2014.
In anticipation of the offensive to dislodge them from Mosul, ISIL fighters have placed booby-traps across the city, dug tunnels, and recruited children as spies, according to Iraqi and US officials.