The Paris high-speed railway network on July 26 was hit by a "massive" and "coordinated" arson attack just hours before the opening ceremony of the city's 2024 Olympic Games.
According to the state-owned railway operator SNCF, vandals damaged signal boxes on three lines connecting the French capital with other major cities, while a fourth attempt was foiled.
"This is a massive attack on a large scale to paralyze the TGV network," SNCF told the AFP news agency.
SNCF said some 800,000 people had been affected by the disruption.
Security sources told Reuters that hardline leftist militants or environmental activists could be behind the attacks, which came just days after French police arrested a Russian man suspected of plotting destabilizing activities during the Paris Olympics.
An anonymous source in the state prosecution service told AFP that an investigation was launched into "sharing intelligence with a foreign power to incite hostilities in France.”