PARIS — One of President Emmanuel Macron’s top security officers was at the centre of an escalating scandal for the French leader on Thursday after being filmed assaulting a protester during a May Day demonstration.

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

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

The presidential palace added that Benalla was suspended without pay for two weeks after the incident and had been transferred to an administrative role instead of 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 euros.

On Thursday evening it was announced that the Law Commission of the National Assembly will hold an inquiry into the Benalla incident.

Interior Minister Gerard Collomb confirmed in parliament earlier in the day that Benalla had "no right to intervene" at the gathering of leftwing student protestors on the Rue Mouffetard, a picturesque Left Bank street loved by tourists.

Macron’s political opponents seized on the footage, asking why the security advisor had not been sacked or reported to the police over the clash.

In a further potentially damaging twist, the BFM news channel reported that Benalla had been back on duty doing security work this week during a victory parade by France’s World Cup-winning football team.

Asked about the video and the investigation during a visit to southwest France on Thursday, Macron repeatedly refused to comment, saying "I’m here with the people" and denying that the image of the state had been damaged.

The French republic was "unalterable," he said.Benalla was the head of security during Macron’s successful election campaign last year, usually found several steps behind the then-candidate. He transferred to the presidential staff in May 2017. — AFP