Arsonists attacked France's high-speed rail network early Friday, setting fires that paralyzed train travel to Paris for some 800,000 people across Europe, including athletes heading to the opening ceremony of the Olympic Games.

Targeting remote locations far from the capital, the apparently co-ordinated attacks sought to cut off rail routes into the city from all directions. The fires were predominantly set in pipes containing critical signaling cables for the system known as the TGV.

There were no reports of injuries. Paris Mayor Anne Hidalgo said the damage would not affect the ceremony, in which 7,000 Olympic athletes were due to sail down the Seine past iconic Parisian monuments such as Notre-Dame Cathedral, the Louvre Museum and the Musee d'Orsay.

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Disrupted train network strands passengers in France

After vandals targeted the high-speed train network in France, the train system was halted while repairs were underway. Crowds of passengers in Montparnasse station were forced to wait for updates to their itineraries as all trains were directed back to their point of departure.

Fires were reported before dawn near the tracks on three separate lines, causing widespread disruptions. Another arson attempt, in the south in Vergigny, was thwarted by rail agents who scared off several suspects.

French authorities did not publicly comment on who might have carried out the attacks or why; none of them said the sabotage was directly related to the Games.

French Prime Minister Gabriel Attal said intelligence services were mobilized to find the arsonists, whose attacks he described as "premeditated" and "calculated."

The evidence indicates "a desire to seriously harm" the French people, said the CEO of national railway company SNCF, Jean-Pierre Farandou, who estimated the number of customers affected at 800,000.

"The places were especially chosen to have the most serious impact, since each fire cut off two lines."

The rail company said in a statement Friday evening that it would ensure transport for all Olympic delegations, without elaborating. It stepped up ground and air surveillance, including with 50 drones.

Prosecutors in Paris opened a national investigation, saying the crimes included property damage threatening the nation's "fundamental interests" and could carry prison sentences of up to 20 years.

German athletes abandon trip to opening ceremony

Two out of four trains carrying athletes to Paris on the western line were stopped hours before the opening ceremony, an SNCF official said.

Two German athletes who were on a Paris-bound train for the opening ceremony had to turn back in Belgium because of the closures, German news agency dpa reported. Repairs were being made as police conducted forensic tests.

"We have to repair cable by cable, so it's very meticulous work," Farandou, the SCNF executive, said.

French Transport Minister Patrice Vergriete said train traffic began to resume in the afternoon.

Rail officials said they expected most trains to be working again Saturday, with possible delays. Some disruptions were likely to continue into Sunday.

The attack occurred against a backdrop of global tensions and heightened security measures as the city prepared for the 2024 Olympic Games.

French authorities have said they foiled several plots to disrupt the Olympics.

Police head to Paris stations

The Paris police prefecture "concentrated its personnel in Parisian train stations" after the attack, Laurent Nunez, the Paris police chief, told France Info television.

In the capital, 35,000 police officers are being deployed each day for the Olympics, with a peak of 45,000 for the opening ceremony.

Paris has been the target of deadly terror attacks in the past decade, and some French officials saw the Games as a chance for the nation to heal from years of trauma.

The disruptions hit Montparnasse station in central Paris particularly hard.

In the station's crowded hall, Maiwenn Labbé-Sorin said she spent hours stranded on a train before it doubled back to Paris.

"We stayed two hours without water, without toilets, without electricity," she said. "Then we could go out on the track for a bit, and then the train returned. Now I'm not sure what's going to happen."

Many passengers at the Gare du Nord, one of Europe's busiest train stations, were looking for answers and solutions on Friday morning. All eyes were on the central message boards as most services to northern France, Belgium and the United Kingdom were delayed.

"It's a hell of a way to start the Olympics," said Sarah Moseley, 42, as she learned that her train to London was an hour late.