French minister urges caution as train derailment probe continues

France's interior minister urged caution on Sunday as authorities investigated the derailment of a train that injured 44 people, amid questions over whether the incident could amount to an act of sabotage.

The train, carrying 186 passengers, derailed on Friday between the Normandy cities of Rouen and Caen in northwestern France, leaving many badly shaken, officials said. 

Prosecutors added that a section of rail found on the track may have caused the derailment.

Herve Morin, president of the Normandy region, said the rail fragment found on the tracks weighed around 300 kilograms.

A source within the railway industry, speaking to Agence France-Presse (AFP) on Sunday, said questions remained over the presence of the rail section, which they estimated at around 300 to 350 kilograms.

The source added that the track had been used "an hour earlier by a train travelling in the same direction" and "half an hour earlier by a train going the other way." 

"The driver of that train saw nothing, even though train crews are instructed to watch for and report anomalies," the source said, noting there was no maintenance work at the site at the time.

"Early evidence suggests that whoever did this followed the train service's schedule to avoid being detected. There had to be several of them to move that section of track," the source added. 

Prosecutor Sebastien Gallois said on Saturday that the reason for the rail fragment's presence on the tracks remained unclear.