French transport was thrust into chaos Friday just hours ahead of the Olympics 2024 opening ceremony after a series of coordinated "malicious acts” upended high-speed train lines.

Officials said the arson attacks and other vandalism on the rail system were a form of sabotage on a pivotal day of the Games. There was no sign of a direct connection to the Olympics, but authorities are investigating.

Travel for hundreds of thousands of travelers was disrupted on the rail system linking Paris to the rest of France and to neighboring countries. No injuries have been reported.

Here is what to know:

What happened to the rail network?

Details were still emerging, but officials say that there were arson attacks and other “criminal acts” of vandalism.

Transport Minister Patrice Vergriete said people fled fires and incendiary devices were discovered. Authorities said they had found at least three fires, triggering disruptions especially affecting Paris' Montparnasse station.

“Everything indicates that these are criminal fires,” Vergriete said.

French Prime Minister Gabriel Attal said intelligence services are trying to find the perpetrators of “acts of sabotage” that he called “prepared and coordinated.”

They happened against a backdrop of global tensions and heightened security measures in Paris as the city prepared for the 2024 Olympic Games.

Paris prosecutors launched investigations into crimes that could carry 15- to 20-year prison sentences.

Jean-Pierre Farandou, CEO of rail company SNCF, said on French TV network BFMTV that the acts showed “a desire to seriously harm” the French and that their nature implied “a premeditated, calculated, coordinated attack.”

How will arson attacks affect the 2024 Olympics?

French trains and the larger transport system faced delays, with some trips taking hours longer than they normally do or halted altogether.

The delays rippled out internationally to stations in London. Many travelers were planning to converge on Paris for the opening ceremony, and many vacationers — including Parisians hoping to escape the Olympics — were also in transit.

A SNCF official on Atlantique line says two of its trains carrying athletes to the Olympics were stopped, including one journey that was canceled.

Two German athletes in showjumping said they will miss the opening ceremonies because of lengthy delays, German news agency dpa reported.

“It's a real shame, but we would have arrived too late,” said rider Philipp Weishaupt, who was traveling with teammate Christian Kukuk. “There was no longer a chance of making it on time.”

The train company said it did not know when traffic would resume and feared that disruptions would last “at least all weekend” as it makes repairs.

SNCF advised passengers to postpone their journeys and avoid going to stations, saying all tickets were exchangeable and refundable.

Who is behind the sabotage?

So far, French authorities have not said who is suspected of plotting and executing the arson attacks.

Asked about whether they could be linked to Russia, French Sports Minister Amelie Oudea-Castera said “maybe,” adding that the attacks could also have been homegrown. She called them “malicious acts.”

Other French officials said it was too early to say whether there is any Russian connection.

The reason people are asking that question is that French officials and cybersecurity experts in the U.S. and Europe have identified an intensifying effort from Russia to undermine France, particularly the Olympic Games, and President Emmanuel Macron, who is one of Ukraine's most vocal supporters in Europe.

Also, French authorities have foiled several plots to disrupt the Olympics, including arresting a Russian man this week on suspicion of planning to destabilize the games.

How important are the Games to Paris?

The train disruptions mark a rocky start to the biggest event France has ever organized. The Olympics are a pivotal moment for Macron, who his facing political turmoil after recent legislative elections.

Macron is welcoming over 110 heads of state and government Friday for the opening ceremony and championed a summit a day earlier where world and business leaders pledged billions in financing to support sporting initiatives aimed at accelerating sustainable development.

The Olympics are the best way to convince the world to “choose France,” Macron said this week, trotting out a motto geared toward boosting foreign investment in the country. “It will promote our landscapes, our facilities, our savoir-faire as well, our gastronomy.”

Friday's grandiose opening ceremony was set to welcome the world, but the train line failures and expected storms appear to be quite literally raining on Macron's parade.