A 2019 crash involving two French defence helicopters in conflict-torn Mali which killed 13 soldiers was due to miscommunication during a military operation, an official report published on Saturday said.

The night accident occurred in November 2019 while the helicopters, both flying at low altitude, were reinforcing ground troops pursuing insurgents near the borders of Burkina Faso and Niger.

A Tiger attack helicopter collided with a Cougar military transport helicopter while engaging the insurgents fleeing on motorcycles and in pick-up trucks.

All those on board were killed.       

"The crews did not detect the presence of the other helicopter. Their reading of the situation was faulty," said a report by the military wing of the Bureau of Enquiry and Analysis for State Aviation (BAE-E).

It said the causes for the accident "were exclusively organisational and human", singling out "faulty prioritisation between the operational objectives of the mission on the one hand and security measures... on the other."

The helicopters came from two different bases in the cities of Gao and Menaka and the pilots and the crew did not receive a common security briefing."

It said the teams were suffering from stress and their messages to each other were imprecise.

"Radio messages between the helicopters minutes before the crash reveal a disorderly and flawed security communication," it added.

Mali has struggled to quell a jihadist insurgency that first emerged in 2012, before spreading to the centre of the country and neighbouring Burkina Faso and Niger. 

France intervened in its former colony to beat back the jihadists in 2013, and now has some 5,100 soldiers deployed across the semi-arid Sahel region.

The crash constituted one of the biggest losses for the French army since a bombing in 1983 in Beirut in which 58 soldiers perished.

Nineteen French soldiers were killed in a 1986 crash in Djibouti.