French President Nicolas Sarkozy blamed "unacceptable negligence" on Monday for an accident at the weekend in which a soldier fired live ammunition instead of blanks, wounding 17 people.

An inquiry has been launched into the incident, which occurred during a combat simulation by the Third Marine Parachute regiment, open to the public in the southern French town of Carcassonne. The soldier is being questioned by police.

"I am appalled. It isn't normal," Sarkozy said during a visit to the hospital in Carcassonne where some of the wounded were being treated. He said those responsible for "unacceptable negligence" should be punished.

"My reaction will be rapid and severe . The whole chain (of command) will have to explain itself, not just one person."

The wounded were mostly members of the public who had been watching the soldiers simulate an attack, including a 3-year-old boy who was hit in the heart and in the arm. Doctors performed an operation overnight and his condition had stabilised.

The chief prosecutor dealing with the case, Brice Robin, told reporters the soldier had said during questioning he made a mistake when he re-loaded his weapon.

"It was not a pre-meditated act, I'm very clear about that. It was a blunder, a human error, a major imprudence, but there was no intention to cause harm," Robin said.

Officials said the soldier had over seven years of experience and had always received good grades for his performance. He had no previous blemish on his record.

Defence Minister Herve Morin told France Info radio it was too early to say how the accident happened but added: "What is certain is that there were errors, procedural lapses."

An official in the army's communications division said the inquiry would determine why the solider had been carrying live ammunition and the circumstances which led to them being used.

Four people, including the 3-year-old boy who had been watching the military show, were severely wounded. An official in a Toulouse hospital where the boy was being treated said his condition had stabilised.