The cause of the accident was still unclear, and the helicopters were not equipped with "black box" data recorders that might have explained what happened.
Five army officers were killed on Friday after two training helicopters crashed into each other near a lake in southern France, officials said, one of the deadliest such accidents involving the country's armed forces in recent years.
The collision took place near the lake of Carces, about 50 kilometres (30 miles) northwest of the resort of Saint-Tropez, just a few minutes after takeoff at 0730 GMT.
All three people aboard one craft, and the two in the other, perished in the crash, the Marseille prosecutor Xavier Tarabeux said on Friday.
The cause of the accident was still unclear, and Tarabeux said the helicopters were not equipped with "black box" data recorders that might have explained what happened.
But he said that the three instructors involved in the exercise were "experienced" as were the two trainees who were with them, and that investigators had excluded the possibility that the helicopters had hit a power line.
A director at the nearby EALAT light-aircraft training school where the two Gazelle helicopters were based said the two instructors at the controls each had 3,000 to 5,000 hours of flight on their record.
"I don't think it's a pilot error - maybe a lapse of concentration, or a mechanical problem," he said.
The two aircraft were discovered about 600 metres apart, one having crashed onto a road and the other in a forest, Tarabeux said at a press conference on a tarmac at the EALAT school alongside defence minister Florence Parly.
One helicopter shattered on impact, spreading debris across a wide area, while the other burst into flames when it hit the ground.
Parly said it was "a day of mourning for all in the defence community, which stands alongside the brothers in arms, the friends and the families of the victims".
President Emmanuel Macron hailed the "commitment of these officers who were preparing themselves for future missions".
The French-made Gazelle helicopters entered service in the 1970s, and are used for reconnaissance and light attacks as well as training.
More than two dozen Gazelles are stationed at the Lejay school at the Cannet-des-Maures base, along with Fennec and Puma choppers.
A local councillor, Jean-Pierre Veran, said helicopters "regularly" fly over the zone and there had never been an accident, calling it a "terrible shock" with debris spread over a large area.
Army chief of staff Jean-Pierre Bosser expressed his "solidarity with the family and friends of the victims, as well as their comrades" at the training facility.
The last major aviation accident involving the security forces in France took place in May 2016, when a police helicopter crashed near Cauterets in the Pyrenees mountains, killing four on board.
An investigation later determined it was caused by pilot error.