“Solidarity with our British friends, horribly attacked, full support for the injured French pupils, their families and their friends,” he said in a tweet.
Foreign ministry spokesman Romain Nadal said three injured pupils were from a high school in Concarneau, in the western Brittany region. Two are believed to be critically injured.
Local radio France Bleu said around a dozen students were on the bridge at the time of the attack, and that the three injured were taken to hospital.
A local newspaper, Le Telegramme, also said the students were on the bridge when they were hit by the car, quoting another student who said the force of the impact threw one of them onto the bonnet of the vehicle.
An official at their school in the town of Concarneau said families of the pupils, aged around 14, were in contact with the London hospital where they were being treated.
They were part of a group of 92 or 93 students, the school official said.
Police and the regional council said family members would be flown to London from the town of Lorient to be with the students.
French president François Hollande sent a message of support to London saying: “Terrorism affects us all. France knows the how the British people are suffering today.”
— Élysée (@Elysee) March 22, 2017
A woman and a British police officer died in the attack at the Houses of Parliament and Westminster Bridge on Wednesday afternoon, while 20 others were left seriously injured.
Later on Wednesday police said the death toll had risen to four.
The assailant was shot dead by police.