On the morning of the Opening Ceremonies, signaling the start of the 2024 Olympic Games in Paris, arsonists attacked the country’s main high-speed railways.

An investigation is ongoing into the attacks, but officials say the damage is done—transportation in and out of Paris is going to be tricky over the coming days, including for the Olympic athletes and spectators attempting to access sport venues.

Two out of four trains taking Olympic athletes to Paris on the western Atlantique high-speed line were stopped for hours Friday, officials with the rail operator told the press. German show jumpers Philipp Weishaupt and Christian Kukuk were on a train to Paris for the opening ceremonies but were turned back in Belgium because of the rail closures, the German news agency dpa reported.

Several Olympic sports and events—including the equestrian competitions being held at Versailles—are taking place outside the city of Paris. Additional Games sites are clustered in Nantes and Bordeaux, which are most commonly accessible by rail.

Eurostar trains, which connects cities like London to Paris are also affected by the attacks. French officials estimate the railway fires are impacting travel plans of 800,000 people.

Despite the delays, Paris Mayor Anne Hidalgo told reporters that the attacks would have “no impact on the opening ceremony.” There were no reported injuries tied to the attacks.

It was “a premeditated, calculated, coordinated attack” that indicates “a desire to seriously harm” the French people, said the CEO of the national railway company SNCF, Jean-Pierre Farandou. SNCF officials were working diligently Friday to get the high-speed lines repaired and restored.

It is unclear who is responsible or the motivation behind the acts.

French Prime Minister Gabriel Attal described the attacks as “acts of sabotage” and “prepared and coordinated.” But he said the objective was clear: “blocking the high-speed train network” by strategically targeting routes from the north, east and west toward Paris at hours just before the start of the Olympic Games.

The Olympics opening ceremony will take place on the Seine River in Paris tonight (or 1:30 p.m. EST). Thousands of police, military and private security are expected to be deployed to secure the event. Some outlets have reported sniper agents on rooftops, fenced-in city streets with highly patrolled armed guards and drones flying overhead of Paris ahead of the Games.