Bastille Day is being marked with the traditional military parade in Paris while France mourns those who died in Friday's rail disaster.
Nearly 5,000 military personnel are taking part on the Champs Elysees along with President Francois Hollande.
Mr Hollande is expected to face questions about the rail accident in a TV interview soon after the parade.
Six people were killed in the crash near Paris, which has raised questions about the state of the rail system.
Fighter jets trailing red, white and blue smoke - the colours of the French flag - streaked over the Arc de Triomphe as the annual Bastille Day celebrations began.
Fifty-eight planes, 35 helicopters and 265 military vehicles are taking part. Mr Hollande was driven in an open-top jeep down the Champs Elysees as troops saluted.
The parade was led by troops from Mali, along with French troops who took part in the country's intervention there to repel an Islamist insurgency.
The 14 July celebrations mark the start of the French Revolution in 1789 when the Bastille prison was stormed.
In a set-piece interview on the main national TV networks, the president is thought likely to try to reassure the French people about the state of the rail network after indications a fault on the track was to blame for the accident.
Mr Hollande is also expected to try to signal that the French economy is recovering and the government is implementing the right policies to tackle unemployment.
Giving its initial findings on Saturday, SNCF said a metal bar connecting two rails had become detached at points 200m outside the Bretigny-sur-Orge station.
"It moved into the centre of the switch and in this position it prevented the normal passage of the train's wheels and it may have caused the derailment," said Pierre Izard, SNCF's general manager for infrastructure.
Carriages were thrown off the tracks - one mounting a platform - as the train passed through the station at 137km/h (85mph).
Transport routes were particularly busy at the time of the crash, as France began the long holiday weekend.
Those killed were four men and two women, aged between 19 and 82. Thirty people were injured, eight seriously.
A large crane arrived at the site on Saturday evening to lift away the remains of carriages, and to find out whether there are still bodies lying beneath.
French media are reporting that it could still take a number of days to clear the derailed cars.
SNCF said 385 passengers were on board when the train crashed and the station platforms were crowded.
Eye witnesses described the train flying into the air and flipping over. Some said it was like scenes from a "war zone" with people running and screaming.
Transport Minister Frederic Cuvillier has praised the driver of the train on Saturday, saying his quick actions averted a worse accident.
Mr Cuvillier said the driver had "absolutely extraordinary reflexes in that he sounded the alarm immediately, preventing a collision with another train coming in the opposite direction and which would have hit the derailing carriages within seconds".
The worst railway accident in France in living memory took place at the Gare de Lyon in Paris in 1988, when two trains collided, killing 56 people.