The man, who was detained at Oissel in northern France yesterday, had access keys to SNCF technical premises, tools, and literature linked to the ultra-left, said the source, asking not to be named.

He was placed in police custody for questioning in Rouen, the main city of France’s Normandy region.

Meanwhile in a new incident, fibre optic networks of several telecommunications operators have been “sabotaged” in six areas of France but Paris is not affected, police said.

Unknown individuals had early Friday attacked three different railway installations in different parts of France, causing days of chaos on the high-speed network as Paris hosts the 2024 Olympic Games.

Interior minister Gerald Darmanin told France 2 television that the authorities were looking into the theory that ultra-left wing movements were behind the attacks.

French services have “identified a certain number of profiles that could have committed” the sabotage acts, he said.

He said the “attacks were intentional, very precise, extremely well-targeted”, adding that this was “the traditional mode of operation of the ultra-left.”

“The question is whether they were manipulated or is it for their own account”, he added.

By Monday morning all high speed trains in France were finally running normally again after railway engineers worked round the clock to repair the damage, said transport minister Patrice Vergriete.

The cost of the sabotage will “very probably” amount to millions of euros, including “commercial losses” and “repair costs”, the minister told RTL.

Fibre optic cables running near the tracks to ensure the transmission of safety information for drivers, such as signalling lights and points, were cut and set on fire in the attacks on three of the main high speed TGV lines, in the west, north and east of France.