The Olympics Rings are displayed on the Eiffel Tower before the opening ceremony of the Paris 2024 Olympic Games, in Paris, France, on 25 July 2024. (Photo: EPA-EFE/Ali Haider) 
The coordinated sabotage took place as France rolled out an unprecedented peacetime security operation involving tens of thousands of police and soldiers to lock down the capital for the Games, sucking in security resources from across the country.
The state-owned railway operator said vandals had damaged signal boxes along the lines connecting Paris with cities such as Lille in the north, Bordeaux in the west and Strasbourg in the east. Another attack on the Paris-Marseille line was foiled.
Hundreds of thousands of people were left stranded at railway stations.
There was no immediate claim of responsibility. But two security sources said initial suspicions fell on hardline leftist militants or environmental activists.
"Everything leads us to believe that these were criminal acts," Transport Minister Patrice Vergriete told reporters at the Gare du Nord.
The coordinated strikes on the rail network will feed into a sense of apprehension before the Olympics opening ceremony in the heart of Paris later on Friday.
Global audience of billions
More than 300,000 spectators are expected to line the banks of the River Seine when the athletes parade through the heart of Paris on a flotilla of barges and riverboats, part of an extravagant opening ceremony that will be watched by a global audience of billions.
Rail company SNCF urged all travellers to postpone their journeys. Repairs were under way but traffic would be severely disrupted until at least the end of the weekend. Trains were being sent back to their points of departure.
The attacks hit signalling installations on the Atlantic, Northern and Eastern high-speed lines with fires set off by explosive devices, the rail authority said.
Company chief executive Jean-Pierre Farandou said about 800,000 customers had been affected before a busy weekend for French holidaymakers. Thousands of rail staff had been deployed to repair the damage.
Destabilising France
"This attack is not a coincidence, it's an effort to destabilise France," Valérie Pécresse, the president of the Paris region, told reporters.
France is deploying 45,000 police, 10,000 soldiers and 2,000 private security agents to secure the opening ceremony. Snipers will be on rooftops with drones keeping watch from the air.
But while the capital is locked down for the opening ceremony, security elsewhere in the country is lighter.
Paris 2024 said it was working closely with the rail authority to assess the situation. The attacks will make it tougher for people travelling to Paris from other areas of France. Some teams like the US basketball team are based in Paris and would have travelled on Saturday by train to the northern city of Lille.
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The Paris police chief said he was beefing up security even further at the capital's main stations. The stations were packed with passengers. Many were preparing to go off on their summer holidays and some had already been waiting several hours.
At the Gare de L'Est, traveller Corinne Lecocq said her train to Strasbourg on the border with Germany had been cancelled.
"We'll take the slow line," she said. "I'm on holiday so it's okay, even if it is irritating to be late."
Xavier Hiegel, 39, said he was just trying to get home for the weekend and could not believe that people would want to harm the Olympics.
"The Games bring jobs so this really is nonsense. I hope the people responsible will be found and punished," he said. Reuters/DM