CARCASSONNE, France  - A French soldier shot and wounded 17 people, including five children, when he fired live rounds instead of blanks at visitors watching a hostage-taking exercise in an army barracks. "Suddenly, people were falling, we thought it was part of the exercise, and then we saw blood," one witness told AFP on Monday. A senior army officer insisted that the incident Sunday at a barracks near the southwestern city of Carcassonne was almost certainly the result of an "unintentional" error. Fifteen civilians were among those injured, including a three-year-old boy and a six-year-old girl who were both operated on overnight and were described Monday as being in a stable condition. Two soldiers were also injured. The soldier who fired the shots, a sergeant described as experienced with no history of behavioural or psychological problems, was detained following the incident.  An army source said three other soldiers were also detained. The eyewitness who spoke to AFP, who asked not to be named, said there were seven or eight soldiers with guns taking part in the exercise, with one of them in the middle of the hundreds of spectators pretending to be a terrorist. Immediately after the real shots were fired, "an official shouted out over the loudspeakers "Cease fire", he said. The use of the live rounds was "99.9 per cent" likely to be "an unintentional fault," said Colonel Benoit Royal, the head of the French army's information service. Military and civilian investigators immediately opened probes into the events at the Third Marine Parachute Regiment barracks. "I cannot rule out anything because we don't know what might be going on in a man's head," Defence Minister Herve Morin said on France Info radio. He said the shooter had first fired a magazine of blanks and then loaded a fresh magazine but this time with live bullets. "Why did he have it in his pocket?" he asked. He said an experienced soldier would not confuse blanks and real bullets, noting that the two munitions are packed into different-coloured magazines. The senior official for the Aude region where Carcassonne is located, Bernard Lemaire, said that investigators believed the deadly ammunition was loaded by mistake. "The question being asked is 'Did the soldier engage in a criminal act or not?'," Lemaire said. "For now, no one can answer that, but the theory being worked on is one of error." French President Nicolas Sarkozy was due to visit the injured in the hospitals in Carcassonne and Toulouse, his office said. Gilles Hulard, a doctor from Carcassonne's rescue service, said the injured had received first aid within three to four minutes of the shooting. The Third Marine Parachute Regiment based outside of Carcassonne numbers 1,200 troops.