By Saskya Vandoorne and Laura Smith-Spark, CNN

(CNN) -- French President Emmanuel Macron is facing a growing crisis as prosecutors confirmed they were investigating a senior aide who was filmed beating up a May Day protester while wearing police insignia.

Alexandre Benalla, a senior security adviser, was taken into police custody Friday after videos emerged that showed him violently confronting demonstrators, with other police officers close by.

The Paris prosecutor has opened a preliminary inquiry into a number of potential charges against him, including violence by a public official, pretending to be a police officer, illegally wearing police insignia and complicity in an attempt to obtain security camera footage.

Another bodyguard, Vincent Crase, who worked for Macron's En Marche! political movement, was also in custody, facing charges of violence by a public official and pretending to be a police officer.

Macron's chief of staff, Patrick Strzoda, was interviewed as a witness by investigators Friday, according to the Élysée.

"The presidency decided to start Alexandre Benalla's dismissal procedure after new facts that could constitute misdemeanor were brought to the president's attention," the Élysée Palace said in a statement Friday.

Speaking Friday evening, Prime Minister Edouard Philippe said that the videos showed "unacceptable behavior that has been punished."

The crisis erupted when a French newspaper, Le Monde, identified Benella and Crase in a video taken at May Day protestors, where riot police were quelling demonstrations with tear gas.

The video shows Benalla lifting a protester off the ground by his neck and covering the man's mouth before striking him over the head with his fist. In another video, he can be seen dragging a young woman towards a wall and trying to force her to sit down, before returning to the young man. Police officers nearby do not appear to make any attempt to intervene.

Macron's office confirmed that dismissal proceedings were under way against Benalla on Friday after "new facts" came to light.

But the Élysée was facing questions over how a senior member of Macron's inner circle could have ended up posing as a police officer and beating up protesters, and why other officers did not stop him. The Élysée is also accused of failing to act quickly enough: Bernalla had already been suspended for 15 days before his dismissal was announced.

Three Paris police officers have been suspended on suspicion of unauthorized communication of surveillance footage to a third party, the French Ministry of Interior said in a statement Friday. The ministry declined to specify who the third party was.

Interior Minister Gérard Collomb "strongly condemns these actions which, if they are confirmed, constitute a serious breach of ethics and undermine the exemplary image which must, in all circumstances, characterize the action of the national police," the statement said.

Collomb is due to appear before a group of senators Tuesday evening to explain Benalla's involvement in the police operations on May 1, according to a statement from the Senate Law Commission Friday.

Benoît Hamon, the former presidential candidate, wrote on Twitter that Collomb should resign, saying that he was "unworthy of his office" and that he had "undermined the foundations of our democracy."

In the National Assembly, Christian Jacob, President of the Les Républicains group, said "the very core of the state has been tainted." He called on Prime Minister Philippe to appear before the assembly and explain what had happened.

'Very aggressive'

Benalla had apparently been invited to observe the demonstrations on May 1 in Paris alongside France's riot police.

Activist Taha Bouhafs, who was demonstrating at the protest, captured the incident on his phone.

In an interview with France's SUD Radio on Thursday, Bouhafs said the protest, which was organized in the capital's Latin Quarter, went from a "convivial" atmosphere to a violent one after riot police used tear gas on the crowd and began hitting people with batons.

Bouhafs said he had seen Benalla at various moments throughout the protest wearing a police armband and assumed he was a policeman or a member of special security forces. "I never thought he was someone who worked with Emmanuel Macron," Bouhafs said.

When the 21-year-old saw Benalla grab a woman by the neck and attack an already "neutralized" male protester, he decided to confront him on camera.

"He was very aggressive. There was no reason for this violence. The man was not dangerous, he was on the ground and begging him to stop. Everyone around him, me included, asked Alexandre Benalla to stop. I said, 'Stop! Stop!' Then he stopped and I got closer and filmed his face and said, 'Look at this face. He did this.' And then he fled."

More claims made against Benalla

Reports have also emerged of previous instances in which Benalla appeared to be heavy-handed.

Political TV channel Public Sénat on Thursday published a video showing Benalla manhandling one of its journalists at a rally in Caen during Macron's 2017 presidential election campaign. Benalla also tore the journalist's press accreditation from him, the channel said.

Public Sénat said it had reported the incident to Macron's En Marche! campaign team but got no response.

Meanwhile, Buzzfeed France published a video that it said showed Benalla removing a communist activist from the 2016 event where Macron declared his candidacy, in the Paris suburb of Bobigny. Buzzfeed quoted the activist as saying Benalla hit him in the head moments after the video ends.

The furor comes as polling suggests Macron's popularity has ebbed since his election.