Anne and Brian Peake, of Barlaston, Staffordshire, were only able to identify their daughter Isabel, 20, from the rings on her fingers after her mutilated body was found by the side of the main Limoges to Paris line last week.

"I'm convinced my daughter did not jump to her death," said Mrs Peake. "She was homesick studying in France, but she was delighted to be coming home to see us.

"She is a dynamic little fighter, not the type to do this sort of thing."

French police say they are keeping an open mind about Miss Peake's death. Clothes and personal effects were found up to six miles down the track, but her handbag and luggage have still not been found.

'Violent impact'

Miss Peake, a third-year student, was just two weeks into an exchange programme at the University of Limoges as part of her four-year undergraduate degree course.

She was returning to Birmingham via Paris and investigators say she had been travelling on the night train from Limoges to Paris.

At a press conference in the town of Chateraoux, inquiry chief Christian Ponsard said: "An autopsy is in progress but preliminary investigations have shown that Isabel suffered an extremely violent impact and that is without a doubt the cause of her death."

He added: "We are led to believe that she fell from a train. Beyond that, all possibilities remain. It is possible it was an accident. It is possible that it was a murder."

'Sexual motive possible'

Miss Peake's body was found clothed in only a T-shirt and underwear, and investigators are looking into the possibility that she was sexually assaulted before her death.

"When you find the body of a 20-year-old woman in suspicious circumstances, you think straight away of a sex attack, but the fact is that I have no proof that it did or did not happen. Examinations are still in progress," Mr Ponsard said.

It is possible that the dead woman's clothes could have been ripped off her body as she fell from the train because of turbulence.

"This is not a criminal investigation yet ... but still an investigation into the cause of Isabel's death," Mr Ponsard stressed.

Train doors 'locked'

But comments by the French railway, SNCF, cast doubt on the theory that Miss Peake was even on the train.

SNCF said the doors of mainline high-speed trains can not be opened between stops and that members of staff were unable to override the safety system.

An SNCF spokesman said it was highly unlikely Miss Peake had fallen from the train she was assumed to be on.

He said that all trains travelling between Limoges and Paris were equipped with a safety system which made it impossible to open a door at speeds of over seven kilometres per hour.

The spokesman said that at the point where Miss Peake's body was discovered trains would normally be travelling at about 160 kilometres per hour.