"There was no other discernible cause," he said.
The train was undergoing a trial on a new high-speed line from Paris to Strasbourg set to open for regular service in April 2016. The train derailed in the village of Eckwersheim, just before the section where the new tracks would link up with the existing network.
The people on board the trial run had included staff from the SNCF railway and their family members and other guests.
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