Cuvillier said the track had been inspected Jan. 14 and there was "no lack of vigilance" on the part of the railway, Radio France Internationale reported.
Four people remained hospitalized as a result of the Saturday mishap in the French Alps, including one in serious condition. Four other victims were released.
Two women died in the accident, a 49-year-old Russian woman on vacation and a local woman in her 80s, RFI said.
Authorities said the 20-ton boulder tumbled down a mountain slope and hit the train.
"It's rainy and snowy in the region and so a boulder was dislodged, rolled down the mountain and collided with the train," Pierrette Ponchon, co-manager of the Hotel Beausejour in nearby Annot, 10 minutes from the site of the derailment, told RFI.
"It's normal for there to be snow at this time of year and sometimes small rocks fall down the mountain, but they're quickly cleared away. So people are surprised, because it's the first time anything like this has happened. They're also shocked, because one of the victims was a woman from Annot, who'd come to live in the town not so long ago."