Heraldo de Madrid - French investigators suspect train derailment was sabotage

The rail fragment was estimated to weigh between 250 and 300 kilograms, and the possibility of a malicious act was being treated as the main line of inquiry.

"The reasons for its presence are unknown and will have to be determined by the investigation," said prosecutor Sebastien Gallois.

Carrying 186 passengers, the train was running between the Normandy cities of Rouen and Caen when it came off the rails around 7:45 pm (1745 GMT) Friday close to Renault's factory in the town of Cleon.

During the derailment, one carriage tipped onto its side while four others left the tracks.

"The most likely scenario at this stage is that this was not simply a malicious act, but one that can be described as criminal," said Herve Morin, president of the Normandy region.

"The locomotive flipped over, meaning the end that had been heading towards Caen ended up facing Rouen, such was the force of the impact."

The section of rail did not "just end up on the tracks like that, given that a train had passed an hour earlier and no maintenance work had been carried out in the meantime", he told AFP.

The maximum speed on that stretch of track was 120 kilometres per hour, Morin added.

Tests on the driver for alcohol and drugs were negative.

Authorities activated a mass-casualty response plan, deploying 130 firefighters, five medical teams and 80 vehicles to the scene.

A mass of railway staff and investigators were seen working around the train on Saturday.

Gallois said 44 people were injured including an 18-year-old woman evacuated "in a critical condition".

She was no longer in life-threatening condition on Saturday but remained hospitalised.

- 'Really shocking' -

Cleon mayor Melanie Delacour said the victims were "in a state of shock."

"The windows of the carriages that remained upright shattered, and because of the train's speed, stones flew into the carriages," she told AFP.

She said that some victims had said they would never take the train again.

"It is a tragedy that could have turned into a disaster on a very large scale," Delacour added.

One of the passengers said the accident was "really shocking."

"Suddenly there were a few jolts, and then after about three seconds it got stronger and stronger," Louis, 24, told ICI Normandie radio.

"I couldn't stay in my seat any more," he said. "The windows partially shattered, the stones from the track came into the carriage," he said.

"I'm still shaking," he added.

SNCF Reseau, which controls the French rail network, initially said that traffic on the line had been suspended and power to the tracks cut to allow emergency services to operate.

According to SNCF, the accident caused "major disruptions" to rail traffic between Rouen and Caen and between Caen and Le Havre in both directions.

A spokesperson for SNCF Reseau said on Saturday that services had resumed.

The train will only be lifted off the line once the public prosecutor allows it, with investigations into the cause of the derailment ongoing.

SNCF said that it would offer "full cooperation in complete transparency" to the inquiry.

L.Herrero--HdM