“Coordinated malicious acts targeted several TGV lines last night and will seriously disrupt traffic until this weekend,” French Transport Minister Patrice Vergriete wrote in a post on the X social network.

Fires were set off at three critical rail-line nodes, with people seen fleeing the sites in vans, Jean-Pierre Farandou, the head of the national rail company SNCF, said on BFM TV. The sites were chosen to have heavy consequences on the traffic, he said. The company will have to repair its network cable by cable, he said, adding that many trains will have to be canceled. About 800,000 passengers will be affected.

“It’s absolutely appalling,” French Sports Minister Amelie Oudea-Castera said on BFM TV. “Acting against the Games is acting against France, it’s acting against your own camp, your own country. They are not the Games of a government, they’re the Games of a nation.”

There have been no official statements over who might be behind the attacks. Paris prosecutors said in a statement that they are investigating the matter.

Over the last few weeks, French government officials have evoked the possibility of the far left or Russia trying to sabotage the Games. Interior Minister Gerald Darmanin told RTL radio on Friday that four attack plans targeting the Olympics had been foiled in the past few weeks by his services.

The disruptions come amid heightened security across Paris, with some 45,000 police and military officials on patrol and barriers set up around the Seine ahead of an opening ceremony that will feature boats sailing down the river, the first of its kind. In preparation, large sections of the city have been cordoned off, with Olympic sites, train stations, tourist landmarks guarded by gun-toting officers, including counter-terrorism units and the military. 

Eurostar said its services to London and Brussels from Paris were affected, and several trains have been canceled or delayed. It said high-speed trains going to and from Paris will be diverted, extending the journey time by around an hour and a half. At Gare du Nord, Paris’s Eurostar train station, a long line of people waited to reschedule their trips. 

Nabeel, a 24-year-old trainee analyst who lives and works in London but had been visiting his family in the Paris region, said he was able to switch to a slightly later train with no problem. He said he was told his trip would take longer than usual.  

“In hindsight, I should have chosen another day,” he said, declining to provide his full name for privacy reasons. 

Meanwhile, chaos reigned at the key Paris rail hub of Montparnasse, with public address announcements reeling off a series of canceled trains.  

“I’ve been here for three hours and I’m going home now,” said Julien Mercier, 29, who was headed to Moreleix in Brittany for a three-day weekend with his parents. Carrying his bicycle in a carry-bag and a backpack, he said he’d try to reschedule for later in the summer. “It is a bit worrying, that they were able to coordinate this, do it today with the Olympics opening and all the security.” 

SNCF said that following the “malicious acts” fast-train services between Paris and several cities had been suspended and that severe delays were expected across its network. 

“Arson attacks were started to damage our facilities, and teams are already on site to carry out the diagnosis and begin repairs,” SNCF said in a statement. The rail company will present a new train re-routing plan later today, France’s caretaker Prime Minister Gabriel Attal said. 

Farandou suggested the attacks were aimed at disrupting the traditional vacation period in France.

They were timed for the “day of big departures,” when a large number of French leave, he said.

“It’s the French that were attacked,” Farandou said.