Saboteurs struck France's TGV high-speed train network in a series of pre-dawn attacks that caused chaos on the country's busiest rail lines ahead of the Paris Olympics opening ceremony on Friday. The coordinated sabotage took place as France rolled out an unprecedented peacetime security operation involving tens of thousands of police and soldiers to lockdown 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 rail 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 ahead of the Olympics opening ceremony in the heart of Paris later on Friday.

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.

The SNCF urged all travelers to postpone their journeys. Repairs were underway 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 signaling installations on the Atlantic, Northern and Eastern high-speed lines with fires set off by explosive devices, the SNCF said.

SNCF chief Jean-Pierre Farandou said some 800,000 customers had been impacted ahead of a busy weekend for French holidaymakers. Thousands of rail staff had been deployed to repair the damage.

"This attack is not a coincidence, it's an effort to destabilize France," Valerie Pecresse, 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 and 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 SNCF to assess the situation. The attacks will make it tougher for people traveling to Paris from other areas of France.

Some teams like the U.S. basketball team are based in Paris and would have traveled on Saturday by train to the northern city of Lille.

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, traveler Corinne Lecocq said her train to Strasbourg on the border with Germany had been canceled.

"We'll take the slow line," she said. "I'm on holiday so it's OK, 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.