Mere hours before the start of the Paris Olympics, a series of pre-dawn arson attacks targeted high-speed rail service across France early Friday, leaving travelers confused and disrupting service ahead of the opening ceremony.

The attacks took place between 1 a.m. and 5:30 a.m. Paris time, the BBC reported. They targeted electrical cables and train signal boxes on three lines of the SNCF, the state-owned railway service. A "large number of trains" were diverted or canceled, SNCF said on X.

As many as 800,000 passengers were affected by the attacks, according to the SNCF, which said the incident was intent on "paralyzing the network," USA TODAY reported. The opening ceremony is expected to take place as planned, with greater security.

Learn more: France rolls out extra security.

No injuries were reported. No one has taken responsibililty for the attacks. Prosecutors have opened a criminal investigation, the Guardian reported.

Damage was found in signal boxes on lines connecting Paris to Lille, Bordeaux and Strasbourg, Reuters reported. Authorities prevented a fourth attack on the Paris-Marseille line.

Many train routes will have to be canceled and repairs would last “at least all weekend,” SNCF told Agence France-Presse. The railway service asked passengers to delay trips and stay away from train stations, Le Monde said. 

SNCF was expected to announce a new transportation plan soon, the BBC said.

Attackers started fires in wire bundles containing multiple fiber-optic cables, Le Monde reported, quoting SNCF CEO Jean-Pierre Farandou. The executive said hundreds of workers would be needed to manually repair the cables one at a time.

Rail disruptions included Eurostar trains running between Paris and London. Other international train routes into France from Germany were also experiencing delays.

The U.S. Olympic and Paralympic Committee said that no American athletes were affected by the train disruptions because they were mostly traveling on buses.

Contributing: Kim Hjelmgaard, Christine Brennan, Jeff Zillgitt, USA TODAY

Source: USA TODAY Network reporting and research; Reuters