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PARIS − Hours before the opening ceremony of the Paris Olympics on Friday, France's national train service said it was targeted by several "malicious acts" that caused disruptions to its high-speed lines.

"Arson attacks were started to damage our facilities," SNCF said in a post on X.

The fires were caused by vandalized signal boxes and electricity pylons at several rural locations outside Paris. However, they had a knock-on impact on services at some of the capital city's main train stations.

The incident comes as French and international security officials have rolled out an extensive security operation for the Olympics involving tens of thousands of extra police and military personnel on the streets.

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The rail service said that up to 800,000 passengers were impacted by the "massive attack" and it asked them to postpone trips. SCNF said the incident was aimed at "paralyzing the network."

SCNF said some overhead cables were cut and burned in what it called an act of "sabotage." The Paris prosecutor's office opened a criminal investigation. There were no immediate claims of responsibility.

One line impacted was between Lille and Paris, a city in northern France where preliminary games of men's and women's basketball and handball knockout stage games are being played.

There were also disruptions to Eurostar trains running between London and Paris. Other international train routes into France from Germany were also experiencing delays.

The U.S. Olympic and Paralympic Committee said that no American athletes were affected by the train disruptions because they were mostly traveling on buses. SCNF said there could be delays through the weekend.

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French and international security officials are on high alert for disruptions to the Olympics. In a Games first, the opening ceremony will take place later Friday outside, along the river Seine. France's capital is in virtual lockdown ahead of that and intelligence gathering on extremist plots and cyberattacks has been boosted.

Organizers have also prepared for the possibility of civil unrest.

French Prime Minister Gabriel Attal warned those responsible that they would face lengthy jail time and substantial fines. In an appearance at the Olympic village, where athletes are staying, International Olympic Committee President Thomas Bach said he didn't have any concerns and had "full confidence in the French authorities."

Contributing: Christine Brennan, Jeff Zillgitt