A teenage protester sparked a security scare in France when he slapped presidential candidate Manuel Valls before he was wrestled to the ground.
Former prime minister Valls, 54, was walking past a group of people in the town of Lamballe, in the Brittany region after coming out of its municipal offices.
He appeared to first shake hands with the youth before the latter shouted: "This is Bretagne!" and reached out to slap the politician.
As Valls recoiled, a security guard seized the youth in a choke-hold, pushed him back against a fence and then forced him to the ground, a video aired by local newspaper Le Telegramme showed.
Police said later the 18-year-old man was in custody.
There is an extreme right-wing local political group in Brittany, a region in France's far northwest, but it was unclear if the detained man was politically motivated, a local prosecutor said.
Valls, a Socialist who is running in the Left's primaries on Sunday to be a candidate for president, did not appear to have been hurt in the incident.
He continued shaking hands, telling the crowd, "it's nothing".
Valls told local reporters later: "I have never been afraid to have contact with the French people. Democracy can never mean violence."