The train crash south of Paris which left six people dead was caused by a fault in the rail tracks, says the state rail company.
SNCF said a metal bar connecting two rails had become detached close to Bretigny-sur-Orge station.
Earlier, Transport Minister Frederic Cuvillier ruled out human error and praised the train driver for averting a worse accident.
Thirty people were injured in the accident, eight of them seriously.
The train had just left Paris on Friday afternoon and was heading for Limoges when it derailed at Bretigny-sur-Orge.
Giving its initial findings, SNCF management told reporters the connector had worked its way loose and become detached at points 200m from Bretigny station causing the train to derail.
The inquiry is now expected to focus on how the piece of metal had become detached, and checks on these components are to be carried out on the whole of the network.
‘Extraordinary reflexes’
Six carriages derailed during the accident at 17:14 (15:14 GMT). The train’s third and fourth carriages derailed first and the others followed. One mounted the station platform.
Aside from SNCF, investigations are being conducted by judicial authorities and France’s BEA safety agency.
Speaking on RTL radio, Mr Cuvillier said the train driver had reacted quickly to the accident: “Fortunately, the driver of the locomotive had absolutely extraordinary reflexes in that he sounded the alarm immediately, preventing a collision with another train coming in the opposite direction and which would have hit the derailing carriages within seconds. So it is not a human problem.”
Local media said a group of people had attempted to steal from the victims shortly after the crash, by pretending to be taking part in the rescue efforts. They reportedly threw stones at emergency workers as they tried to reach passengers.
French transport routes were particularly busy at the time of the crash due to the run-up to a holiday weekend marking Sunday’s Bastille Day. SNCF said 385 passengers were on board when the train crashed. The station platforms were crowded.
French President Francois Hollande visited the scene on Friday evening to express his shock at the accident.
He said that the station would be closed for three days while investigations were carried out.
British student Marvin Khareem Wone was on a train on another platform when the carriages of the intercity ploughed into the station.
“The train went off the railway; it just went on the platform and kind of flew in the air for a second and went upside down,” he told the BBC.
“The first and the second coach were completely destroyed. I really thought no-one could survive that because it was completely mashed up. Everyone was crying and running everywhere. A woman was crying for her daughter who was still on the train.”
‘Images of war’
Because of the damage to the station, he said ambulances could not reach the platform and the lift was not working.
Other media reports spoke of passengers being electrocuted and crushed.
“I saw many wounded women children trapped inside,” Vianey Kalisa, who was waiting for his train from Bretigny to Paris, told AFP.
The train had left Paris-Austerlitz station at 16 :53 local time and was due to arrive at Limoges-Benedictins at 20:05, SNCF said in a statement.
During Saturday, heavy lifting equipment will be used to lift the wreckage of the carriages clear of the rails, says the BBC’s Hugh Schofield in Paris.
Many people feel it was lucky that the accident was not a lot worse, given the violence of the impact and the fact that a packed train ploughed onto the platform at peak time, our correspondent says.
Agencies