It said acts of sabotage overnight, including fires, caused huge delays to TGV services already hit by a long transport union strike over reforms.
The SNCF blamed militants for the attacks, saying they wanted to harm ongoing talks to end the strike.
President Nicolas Sarkozy said the saboteurs would be severely punished.
Millions of French people... are tired of being used as hostages
In a statement, the SNCF said there had been "several acts" occurring "at the same time" on lines in the north, east and south-west of the country.
It said these included a "very large" fire on the TGV's Atlantic branch that damaged signals affecting 30km (18 miles) of track.
Union officials deplored the attacks as acts of vandalism, warning that they put people's safety at risk.
The open-ended rail strike is over planned changes to the pension system by President Nicolas Sarkozy.
Mr Sarkozy has vowed to press on with the reforms.
The TGV network was targeted several hours after French Labour Minister Xavier Bertrand said he hoped that talks between rail unions and the government would help end the strike.
'SPECIAL' PENSIONS SYSTEM
Benefits 1.6m workers, including 1.1m retirees
Applies in 16 sectors, of which rail and utilities employees make up 360,000 people
Account for 6% of total state pension payments
Shortfall costs state 5bn euros (£3.5bn; $6.9bn) a year
Some workers can retire on full pensions aged 50
Awarded to Paris Opera House workers in 1698 by Louis XIV
The talks opened on Wednesday.
"I think the conditions are there for everyone to get out of it honourably," Mr Bertrand was quoted as saying by the AFP news agency.
President Sarkozy also urged the protesters to go back to work now that negotiations were beginning.
"Everyone must ask whether it is right to continue a strike which has already cost users - and strikers - so dear.
"I think of those millions of French people who after a day of work have no bus, metro or train to take them home and who are tired of being used as hostages."
The government has said there could be incentives of salary rises and a top-up scheme for pensions.
But it has stressed that there will be no budging on the core issue of eliminating special pensions which allow 500,000 transport and utility workers to retire early.
Didier Le Rester of France's General Labour Confederation has predicted that the negotiations could last up to a month.
Before the latest incidents, SNCF had estimated there would be slightly improved rail services on Wednesday as the number of strikers steadily declined.
Paris transport operator RATP said about 25% of its metro trains would be running.
The week of strikes has caused havoc for millions of commuters across France.
Businesses have started complaining that the strikes are hurting their operations.
Finance Minister Christine Lagarde said the dispute was costing France up to 400m euros (£290m) a day.
On Tuesday, hundreds of thousands of civil servants joined striking transport and energy workers over what they say is an erosion in their earnings and proposals to slim France's large public sector.
Very large fire reported to have damaged signal equipment affecting 30km of track on the Atlantic line
Signal switches in the South East and East lines reported to have been sabotaged
Fire reported to have damaged signal cables affecting the North line
(此字從法語來的 / 英法語皆同)
( 故意破壞 machine, railway line or bridge / ex. 戰爭中或抗議)
(此字從法語來的 / 英法語皆同) / 故意破壞者
above info from BBC