PARIS, France (CNN) -- Striking railway workers have carried out "a coordinated campaign of sabotage" on the tracks of France's high-speed TGV rail network, setting fire to cables and signal boxes and causing delays of up to three hours, France's national rail authority said Wednesday.
Commuters wait for trains at Paris Saint-Lazare subway station.
The rail authority, government and unions all condemned the acts.
In a statement, the French National Railway Company, SNCF, said the attempts to destroy the lines were aimed at preventing services from resuming.
"These actions are the work of hardliners and show total irresponsibility," the SNCF said.
A large fire on the TGV Atlantic line damaged 30 km (18.6 miles) of cable along the signaling network, forcing high-speed trains to be rerouted along slower lines, the SNCF said.
Several fires along the TGV North and Southeast lines were the result of a rag being set on fire and stuffed inside a cable storage box, the SNCF said, forcing the authority to close signaling switches along the lines.
Another fire along the TGV East line slowed service.
The authority said it dispatched teams to identify the areas of damage and repair them, and that police were also investigating.
"The SNCF is outraged that such irresponsible and illegal actions could happen," the statement said.
French Transport Minister Dominique Bussereau denounced "grave abuses" and described the coordinated character of the acts as "unacceptable."
Unions also condemned the acts of vandalism "committed by cowards."
The attacks come as crippling strikes by transit workers over pension reform plans enter their eighth day.
They are striking over plans by French President Nicolas Sarkozy to reform a special category of pensions. The government is focusing on pension plans which allow some workers -- mostly train drivers -- to retire as early as 50.
Negotiations are expected to begin at 3 pm local time Wednesday between representatives from the unions, the government, and the SNCF.
Sarkozy, who has said he will not give in to the strikers, has enjoyed public support for his planned reforms, but the strikes are being seen as a test of his political will.
While the strike has not caused a complete shutdown of the trains, it has cut enough services to wreak havoc for French commuters.
An increasing number of transportation workers has gradually reported to work, reflecting dwindling support for the strike among both union members and the public.
Wednesday, the SNCF said about 22 percent of its workers were on strike, compared to 27 percent the day before. Throughout the strike, however, the rail authority has expressed concern that hardline members opposed to any negotiations would pose problems.
A train crash Wednesday on the French island of Corsica was not related to the sabotage, the SNCF said.
Two trains collided in the town of Barchetta, on the northern part of the island, injuring 24 people, three of them critically, the SNCF said.
The rail authority said preliminary information indicated human error was to blame. E-mail to a friend
Producer Sammy Berrahmoun contributed to this report.