French authorities on Sunday arrested an activist of an ultra-left movement allegedly linked to the sabotage of the rail network that left more than 800,000 people stranded on the same day as the official opening of Paris 2024.

With the risk of terrorist attacks and sabotage high during the Games, police reported that the cables of several telecommunications operators were sabotaged in six areas of France on Sunday night and Monday, although Paris was not affected.

AFP confirmed with major operators, including Free and SFR, that they had been affected, although no significant disruption had yet been reported.

"It's vandalism," said Nicolas Chatin, spokesman for SFR, one of France's top four operators. "Large sections of cable have been cut. You would have to use an axe or a grinder."

Although they minimised the impact of the disruption, claiming that only 10,000 fixed line customers had been affected, Chatin reiterated: "It's vandalism; large sections of cable have been cut."

Paris chief prosecutor Laure Beccuau said the police had opened a second criminal investigation into the fibre-optic incidents and that the perpetrators were suspected of "causing material damage with the intention of harming the fundamental interests of the nation".

In the first sabotage incident in France, the ultra-left activist was arrested in Oissel, northern France, on Sunday. He was found in possession of access keys to the technical facilities of the Société Nationale des Chemins de fer Français (SNCF), tools and literature linked to the "extreme left", according to anonymous police sources.

The suspect was taken into police custody for questioning in Rouen, the main city in France's Normandy region.

Interior Minister Gerald Darmanin told France 2 television that authorities were investigating the theory that "far-left" movements were behind the attacks. French services had "identified a number of profiles that could have committed the acts of sabotage", the minister said.

"The attacks were very deliberate and targeted. This is the traditional modus operandi of the extreme left," Darmanin said.

"The question is whether they were manipulated by other people or whether they did it on their own," he added. "We are making good progress and we will find them."

Although the minister confirmed that the saboteurs clearly had "information" about the facilities, he declined to comment when asked if he thought the information came from within the SNCF.

An email claiming responsibility for the attacks was obtained by several French media outlets over the weekend, using rhetoric typical of militant groups and criticising the Olympics as a "celebration of nationalism", something the internationalist left has always opposed.

As for the cost of the sabotage, the minister told RTL that it was "very likely" to run into millions of euros, including "commercial losses" and "repair costs".

Fortunately for the public, all high-speed train services in France were back to normal by Monday morning after the tireless work of railway engineers and support staff, according to Transport Minister Patrice Vergriete.

It is still unclear whether the police are linking the sabotage attacks on telecommunications and railway cables. No one has yet claimed responsibility for the sabotage, and the investigation is being conducted under strict secrecy.

Nicolas Guillaume of Netalis, a fibre-optic operator, said: "What makes us angry, frankly, is that we feel the state has not understood the importance of these potential attacks on France's strategic infrastructure. We've already seen it with what happened to the SNCF".