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.According to French police, the "acts of sabotage were prepared and coordinated," indicating a deliberate attempt to create chaos during the event.Targeting remote locations far from the capital, the 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.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.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."In a statement Friday evening, the rail company said 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."Disturbing such a festival of peace with acts of violence can never be accepted and demands the most determined rejection," German Chancellor Olaf Scholz said in Paris.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 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 Games.French authorities have said they foiled several plots to disrupt the Olympics, including arresting a Russian man on suspicion of planning to destabilize the games.Earlier this week, French Interior Minister Gerald Darmanin said about 1,000 people suspected of possibly meddling on behalf of a foreign power have been blocked from attending the Games. Among those blocked were people suspected of Islamic radicalization or left- or right-wing political extremism, or who had significant criminal records, he said.Although he has repeatedly pointed to suspicions of Russia-backed interference, Darmanin added that such threats have also come from other countries that he did not name.The Paris police prefecture "concentrated its personnel" in train stations after the attack, Paris Police Chief Laurent Nuñez 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 Paris' Montparnasse station 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, sought 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.Germany's national railway operator, Deutsche Bahn, said there also were short-notice cancellations and delays between France and Germany.Prominent French cartoonist Plantu found inspiration in the rail network's quick response. He posted a cartoon on Instagram depicting the first three Olympics gold medals going to SNCF agents. Three agents were sketched on the Olympic podium, holding cables and trains, with dangling gold medallions around their necks.Also, on Friday, the French airport of Basel-Mulhouse on the border with Germany and Switzerland was evacuated in the morning and shut down briefly "for safety reasons," the airport said. It wasn't clear whether there was a connection to the rail attacks.