The Olympic Games have been hit by what French authorities are calling "coordinated malicious acts" across the country's high-speed train network.
SNCF, the state-owned railway operator, said arsonists have attacked regional lines connecting Paris with the West, North, and East.
"Fires were deliberately set to damage our installations," it said.
The fires created chaos and caused massive delays across the country on the day the Olympic ceremony was due to begin and disruptions were expected all weekend.
French authorities are calling it a "coordinated sabotage" with the sports minister, Amélie Oudéa-Castéra, saying it is "completely appalling".
"To target the games is to target France," she said.
Oudéa-Castéra said they were working to evaluate the impact on athletes.
France's transport minister Patrice Vergriete strongly condemned the "criminal acts" which would also compromise many holiday plans.
Eurostar also said it had to cancel and delay several of its rail services between London and Paris.
It said in a statement: "Due to coordinated acts of malice in France, affecting the high speed line between Paris and Lille, all high speed trains going to and coming from Paris are being diverted via the classic line today. This extends the journey time by around an hour and a half. Several trains have been cancelled."
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