The train which crashed last Friday in Cameroon was travelling at an "unusually" high speed, a top official of the French company that runs the railway line has said.
The rail accident killed at least 79 passengers and wounded 600 people.
Early suggestions seemed to blame the crash on overcrowding.
But train company Bollore says that the train was still going fast at a point where it was expected to be travelling at lower speed.
The passenger train was travelling from Yaounde, the capital, to the port city of Douala when carriages flipped over at high speed.
Eric Melet, Africa chairman of Bollore, told BBC Afrique the train should not have approached the site where the accident happened without slowing down.
"When it was near the station where the crash happened, it was travelling faster than the speed limit at that point," Mr Melet said.
Shortly after the crash was reported, Cameroon President Paul Biya told state TV that an "in-depth inquiry" into the causes of the accident had been ordered.
On Tuesday, a court also announced a criminal investigation to establish responsibilities in the possible causes of the accident.
The train was operated by Camrail, a local subcontractor of French company Bollore.