The black boxes from two French military helicopters that collided in Mali killing 13 soldiers have been found, a French military spokesman said Wednesday.

The crash occurred on Monday during an operation against jihadists in the restive region. It was the heaviest single loss for the French military in nearly four decades.

"The two black boxes from the helicopters have been recovered, they will be handed over to the relevant authorities to be analysed," the spokesman, Colonel Frederic Barbry said.