A train derailment near Paris that killed six people was caused by a fault in the tracks, France's state rail company says.
The SNCF said Friday's derailment, which also left dozens injured, was caused by a connecting bar that came loose at a rail switch at the station at Bretigny-sur-Orge, about 25 kilometres south of Paris.
The joint bar "broke away, it became detached and came out of its housing", said Pierre Izard, general manager for infrastructure, on Saturday.
It "lodged itself at the centre of the switch, prevented the normal progression of the train's wheels and seems to have caused the train's derailment."
The company said the switch was checked on July 4 and it was immediately ordering checks of 5000 similar joints on its network.
"We have decided to check equipment of this nature on the entire network and are starting now," SNCF chief Guillaume Pepy said.
Transport Minister Frederic Cuvillier said human error was not to blame for the accident, praising the train's driver who he said "had absolutely extraordinary reflexes by sending the alert immediately", preventing a collision with an oncoming train.
But he said France's regional rail lines were out of date.
"We cannot be satisfied with rolling stock that is 30 years old," Cuvillier said, adding: "The situation is severe, with the deterioration in recent years of traditional lines because of a lack of resources."
A railway passenger association also denounced what it called "rust-bucket trains" and the practice of coupling different types of trains together, demanding proper inspections.
President Francois Hollande was likely to face tough questions about the accident on Sunday, when he is expected to be interviewed by leading French television channels to mark the Bastille Day holiday.
A minute of silence was held at noon on Saturday on all French trains and in all stations for the victims of the accident, which took place as many were leaving for summer holidays.
The local prefect's office said the dead were four men and two women, aged between 19 and 82.
A source close to the investigation told AFP the dead included a couple in their 80s from Bretigny, three men aged 19, 23, and 60, and a young woman whose exact age was not immediately clear. Formal identifications of the bodies were underway, the source said.
In what officials described as a "catastrophe", the train came off the tracks and crashed into the station platform at 5.14 pm local time on Friday, as it travelled at 137km/h on its way from Paris to the central western city of Limoges.
Four carriages of the train jumped the tracks, of which three overturned.
One carriage smashed across a platform and came to rest on a parallel track; another lay half-way across the platform. There were 385 passengers on the train.
The local prefect said the death toll of six was final after the first of the four damaged carriages was removed from the tracks.