PARIS -- A rail joint that worked loose from a track switching point appears to have caused France's worst train accident in years, an official with the national rail company said Saturday.
The crowded intercity train, leaving Paris at rush hour before a holiday weekend for the city of Limoges, jumped the tracks 20 miles south at Brétigny-sur-Orge station. The seven-car train split into two, with some cars riding up the station platform and flipping over.
Six people died, two were in critical condition and seven more were in serious condition, officials said; 21 others were still in the hospital. More than 190 people were treated at the site for lesser injuries.
Officials said the death toll might increase as the wreckage was removed because some people might be under the overturned cars.
Railway investigators discovered that a metal clip joining two rails as part of the switch, which guides trains from one track to another, had worked loose and disconnected from its normal position, said Pierre Izard, the director for infrastructure at the national rail company, S.N.C.F.
"It broke away, became detached and came out of its housing," Mr. Izard said at a news conference at the scene. "It moved into the center of the switch, and in this position it prevented the normal passage of the train's wheels and seems to have caused the derailment."
The president of the S.N.C.F., Guillaume Pepy, said engineers would check the condition of 5,000 similar switches along the rail network.
President François Hollande and Prime Minister Jean-Marc Ayrault went to Brétigny-sur-Orge on Friday evening to comfort victims and their families and to thank rescue workers. They promised a full investigation.
The first two cars of the train seemed to have passed along the tracks without difficulty, but the third car was the first to derail, about 200 yards before the station. The train had left Paris 21 minutes before, packed with 385 people, and was not scheduled to stop at the station.
Officials said work had been performed this month on the tracks. They are shared with the suburban railway line, the RER C, which is used heavily and carries an average of 540,000 people a day. The switch was last inspected on July 4, railway officials said, and another train had passed safely over the same tracks a half-hour before.
The minister of transport, Frédéric Cuvillier, said Saturday that he believed the fault was mechanical, not human. He praised the driver of the train for acting quickly to sound an alarm, preventing a collision with another train. He said the train was traveling about 85 miles per hour, under the speed limit: 93 miles per hour.
Mr. Cuvillier said there was no indication that a lack of investment in maintaining the system's infrastructure was at fault. But he said France's regional rail lines were out of date, since the S.N.C.F. had focused so much attention on its high-speed T.G.V. lines, one of France's prides.
"We cannot be satisfied with rolling stock that is 30 years old," Mr. Cuvillier said, adding, "The situation is severe, with the deterioration in recent years of traditional lines because of a lack of resources."
A minute of silence was held at noon on all French trains and in all stations for the victims of the accident.
The six who died -- four men and two women -- were 19 to 82 years old, the police said, without providing names.
The accident is the worst since 2008, when seven students died after a train hit a school bus. France's worst rail disaster in 25 years occurred on June 27, 1988, when one commuter train rammed another on underground lines from Gare de Lyon in Paris, killing 56 people.
Rail traffic remained disrupted over the weekend; the national holiday, Bastille Day, is on Sunday.
This article originally appeared in The New York Times.