Nicolas Sarkozy said he was appalled at the incident
French President Nicolas Sarkozy has called for swift and severe punishment after 17 people were shot during a demonstration at an army open day.
Five children were among those injured after a soldier loaded his gun with live rounds instead of blanks.
The victims included a three-year-old boy, who was hit in the heart, and both of his parents.
Mr Sarkozy said it did not seem to be a deliberate act but that it was the result of "unacceptable negligence".
The president visited the wounded in hospital on Monday - the day after the incident occurred during a public demonstration of hostage-freeing techniques at a barracks in Aude, in the south-west of France.
"I am appalled," the president said. Those responsible should be punished, he said.
"My reaction will be rapid and severe... The whole chain [of command] will have to explain itself, not just one person."
'No psychological problems'
The soldier who fired the shots has been detained.
It is not clear why the wrong ammunition was used in Sunday's demonstration.
But it was "99.9%" likely to be "an unintentional fault," Colonel Benoit Royal, head of the French army's information service, told the AFP news agency.
The regiment is now in the public glare
However, Defence Minister Herve Morin said: "I cannot rule out anything because we don't know what might be going on in a man's head."
He said "an experienced soldier" should not be able to confuse blanks with real bullets.
"According to initial findings of the inquiry, the incident involved a soldier with a perfect record, who had participated in operations and had seven to eight years of experience," he said.
"There is nothing that would make one think he had behavioural or psychological problems," he added.
Reports from the scene say the hostage scenario had been acted out five times before a crowd at the Laperrine military barracks, near Carcassonne, when on the sixth take real bullets began flying through the air, and onlookers fell to the ground.
Fifteen civilians were among the 17 injured.
Hospital officials said the three-year-old boy was operated on overnight and was in a stable condition, and that two of the victims were in a "serious" but stable condition, AFP reported.
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