Macron security official filmed hitting protester

One of President Emmanuel Macron's top security officers was at the centre of a potentially damaging scandal for the French leader on Thursday after being filmed hitting a protester.

Le Monde newspaper published a video showing Alexandre Benalla striking and then stamping on a young man while wearing a police visor during a demonstration in central Paris on May 1.

Benalla, who is not a policeman and previously worked as a bodyguard, had been given permission to "observe police operations" in central Paris during a day off on the May 1 public holiday, Macron's office said.

The presidential palace added that Benalla had been suspended for two weeks after the incident came to light and had been transferred out of his job, which was organising security for Macron's trips.

"This sanction was to punish unacceptable behaviour and it was a final warning before being sacked," presidential spokesman Bruno Roger-Petit told reporters.

Prosecutors in Paris opened a probe on Thursday into possible charges of violence by a public official, of pretending to be a policeman and the illegal use of police insignia.

Imitating a policeman can lead to a prison term of up to a year and a fine of €15,000.

Benalla was the head of security during Macron's successful campaign last year, usually found several steps behind the then-candidate, and transferred to the presidential staff in May 2017.

Asked about the video and the investigation during a visit to southwest France on Thursday, Macron refused to comment, saying only: "I'm here with the people."

The 40-year-old centrist was in Australia on May 1, a traditional day of demonstrations in France organised by trade unions, but which was marred this year by hundreds of black-clad anarchists who clashed with police and smashed up shops.

Macron condemned the violence at the time in a tweet, saying that "everything will be done so that those responsible will be identified and held accountable for their actions."

Opposition MPs suggested Thursday that there had been a cover-up for Benalla and questioned why the incident on the picturesque Rue Mouffetard, several kilometres from the main demonstration, had not been referred to the police when it came to light.

Socialist Party leader Olivier Faure said there was a "double standard" in how Benalla had been treated compared to any ordinary French citizen.

Alexis Corbiere, an MP for the hard-left France Unbowed party, said Benalla "deserves to be punished with a prison sentence, at least a suspended sentence, and with very heavy sanctions."

The man struck by Benalla, who has not been identified, was a member of the party, Corbiere added.

Le Monde quoted a witness of the incident, Jeremie Ferrer-Bartomeu, as saying that it "was a really violent scene, which seemed to be without reason and completely out of blue."

Macron has fallen in the polls recently and has an approval rating in the mid-30s, according to one survey, though analysts said he might benefit from the feelgood factor after France's World Cup victory last weekend.

His supporters claimed that the punishment handed down to Benalla -- suspension without pay for two weeks and a transfer to an administrative job -- was appropriate.

"Someone was found to have unacceptable behaviour and there was a sanction," Social Cohesion Minister Julien Denormandie said on France Inter radio on Thursday. "It was immediate... meaning a suspension and a job change."

Richard Ferrand, a senior MP from Macron's party and a top figure in the campaign team, said "it was not a close aide, it's someone who was responsible for security of the president during the election campaign and then joined the Elysee."

Benalla was suspended from May 4-19.