Speaking after a meeting of the special anti-terrorist committee, Mr Debre admitted that the authorities had no indication of the identity of the bombers. "Until we have the results of the investigation into the explosives and the timing device used," he said, "we cannot commit ourselves to one direction rather than another."
Mr Debre added that until all the dead and injured had been identified, it could not be ruled out that "they included someone who took a direct part in the terrorist act".
The death toll rose to seven yesterday. One of the dead, a man, remains unidentified; the names of the other six - one of Portuguese origin, the rest French - were released last night; 29 of the injured were still in hospital, of whom 11 were in a critical condition.
Throughout yesterday the police and intelligence services mounted a sweeping security operation across France. Special security arrangements were in force at airports, railway stations and public buildings, with 1,800 police and anti-terrorist forces deployed in Paris alone and sniffer dogs much in evidence.
Frontier controls were tightened and identity checks conducted. More than 200 people were stopped in Paris overnight on Tuesday, 80 of whom were found to be in France illegally, according to police. Automatic left- luggage lockers at Paris railway stations and airports were closed; litter bins were removed from public places and police issued an appeal for vigilance.
The atmosphere of nervousness led to false alarms. St-Michel station, the scene of Monday's explosion, and the next station, Chatelet, were closed briefly after bomb scares, as was the Virgin Megastore in the Champs Elysees, and the pyramid at the Louvre.
Marseilles, which has a large north African population, was placed on security alert, with police and riot squad officers patrolling the streets. Bomb scares led to the clearing of Grenoble town hall and the main railway station in central Lyons.
The authorities announced the setting up of an official investigation, under a judge specialising in terrorist cases, Jean-Francois Ricard He stressed that the inquiry would be "long and exhaustive", but said that the priority was to determine the origin of the explosives used in the 3-4kg bomb.
The French media were full of tales of survival and heroism. One man, Thierry Rabdeau, having extricated himself from the wreckage and helped others to safety, was reported to have walked calmly up the station escalator, batting flames as a shocked onlooker told him his trousers were on fire. After phoning to reassure his family, he took the suburban train home, where his family called an ambulance.
"When the train pulled into St-Michel station, I got up and went toward the doors to get off. It was exactly 5:30, I remember. The car was crammed. At the precise moment I touched the door handle, the explosion went off. The doors literally blew to bits, and I was blasted out on to the platform," he told a Paris newspaper, Le Parisien.
After a few seconds, the young industrial designer got up and went back into the train. "All the passengers were on the floor, piled on top of each other, spattered with blood. People were screaming. I don't know how to explain this, but I went back to get my sneaker, which was filled with blood. I tore it out of that pile of bodies."
He was so confused that he just got on the escalator and went to an upper platform to wait for the first train home to the suburbs. It was not until people leapt to help him that he realised his trousers were on fire and his clothes in tatters. "I only had one thought in my head. To get back home to my wife and two kids. Tell them I was alive."
There was praise, too, for the emergency operation co-ordinated by the chief of Paris police, Philippe Massoni. He invoked for the first time anemergency plan involving three separate types of alert: a "railway alert", bringing in specialists from the fire brigade, a "red alert", providing emergency medical staff, including surgeons, trained to deal with disasters, and a "white plan", ensuring immediate evacuation and provision of beds in specialist hospitals for the worst injured. According to satisfied city officials yesterday, the plan "ran like clockwork".Reuse content