Sabotage on the rails jeopardises big day for Paris

But who would want to ruin the plans of hundreds of thousands of French travellers and disrupt the start of the Olympic Games?

One security source suggested in French media that the arson attacks bore all the hallmarks of the extreme left.

However, Mr Attal has refused to speculate who might have been behind the sabotage.

He appealed to the public to be cautious as the investigation is only just starting, although he did say the fact that the saboteurs had targeted “crucial points” on the high-speed network indicated awareness of where it was vulnerable to attack.

In recent weeks, Russia has been linked to at least two alleged plots in France.

Last month, a Russian-Ukrainian national was arrested at a hotel near Charles de Gaulle airport on suspicion of being part of a Russian-sabotage campaign,

Only this week a Russian man was arrested on suspicion of involvement in a “destabilisation” plot targeting the Games.

Interior Minister Gérald Darmanin said he was suspected of aiming to “organise operations of destabilisation, interference, spying” on behalf of Russia’s FSB intelligence service.

So far no Russian link has been made by French authorities to Friday’s attacks.

Mr Darmanin said this month that 3,570 people had been barred from the Games, including people seen as security risks as well as “dozens of radical individuals close to Islamist, ultra-left and ultra-right circles”.

Almost a million people, ranging from athletes and coaches to Olympic volunteers, have gone through a security check ahead of the Games in Paris.

But preventing acts of sabotage at unguarded sites in rural areas is a wholly different prospect.