Coordinated acts of sabotage struck France's high-speed trains, causing further delays to services already widely disrupted by strikes, just as talks were opening Wednesday to coax unions into ending their walkout.

The national SNCF rail authority stopped short of blaming strikers for the overnight vandalism, which it said included the burning of electric cables and damage to signaling systems. Labor unions quickly denied any connection.

Nevertheless, the attacks added a new note of ill will before talks Wednesday between unions and the companies worst hit by the strike — the Paris transit authority and the SNCF.

The SNCF called the vandalism a "coordinated sabotage campaign." The boss of the powerful CGT union, Bernard Thibault, condemned the attacks but also suggested they may have been designed to discredit the strike movement.

Train drivers, Paris Metro employees and certain other public employees have been staying off the job to protest President Nicolas Sarkozy's plan to trim their retirement benefits.

Sarkozy appears to have the upper hand in the test of strength with powerful transport unions: Opinion polls show the public strongly supports the president, and strikers have been trickling back to work on subway and long-distance trains.

Just over half of the 700 usual high-speed trains were scheduled to run Wednesday, the SNCF said. It said the acts of vandalism were causing delays of one to three hours for some high-speed trains.

The attacks appeared to be aimed at further crippling the fast train network: Vandals targeted lines connecting Paris to the western Atlantic coast, the east, the north and the southeast of the country.

Interior Minister Michele Alliot-Marie said police were working to identify those responsible.

Talks between labor unions and Paris' public transit authority kicked off with a government representative present. Negotiations with the SNCF were slated for later Wednesday. The talks are expected to last one month.

The government hopes the opening of the negotiations will prompt a full return to work.

French officials have warned about the strike's effect on the economy, warning it could further slow growth.

The head of France's main employers' association described the strike as "a real catastrophe for our economy."

"The economic cost is incalculable, probably gigantic," Laurence Parisot told RTL radio.