Paris (AFP) - French police held a Russian activist and his girlfriend for questioning on Sunday over sex videos released online that brought down President Emmanuel Macron's favoured candidate for Paris mayor.

Pyotr Pavlensky has said he leaked the video that forced the centrist ruling party's Benjamin Griveaux to bow out of the running for mayor in next month's election.

The artist, who received asylum in France in 2017 after several radical protests in Russia, was arrested on Saturday in connection with a fight at a New Year's party.

On Sunday, however, police turned their attention to the footage posted online this week showing a man masturbating, coupled with racy text messages sent to a woman.

The videos prompted Griveaux, a married father of three, to abruptly call off his mayoral campaign, a first in France, where politicians have in the past attempted to brush off sex scandals as private matters.

Pavlensky's French girlfriend, Alexandra de Taddeo, believed to have been the recipient of the videos sent in 2018, has also been arrested on charges of invasion of privacy and publishing images of a sexual nature without consent.

- 'Political porn' -

Pavlensky, 35, and de Taddeo, 29, were both being questioned on Sunday at the headquarters of the criminal police in Paris.

On Friday, Pavlensky told AFP that he had posted the footage online in order to expose the "hypocrisy" of 42-year-old Griveaux and planned to post more material on a newly created "political porn platform".

Griveaux "is someone who constantly brings up family values, who says he wants to be the mayor of families and always cites his wife and children as an example. But he is doing the opposite," Pavlensky told France's Liberation daily.

Griveaux's lawyer, Richard Malka, hit back on Sunday, accusing "pseudo artists" of giving "morality lessons".

French media and politicians from across the spectrum have portrayed Griveaux, a former government spokesman, as the victim of a hatchet job.

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"Everyone has the right to their secret garden," the speaker of the National Assembly, Richard Ferrand, told the Journal du Dimanche weekly, echoing a sentiment still widely held nine years after politicians' morals came under scrutiny in the Dominique Strauss-Kahn affair.

Griveaux's fall left Macron's Republic on the Move (LREM) party scrambling to find a replacement candidate for Paris mayor a month before the vote.

Health Minister Agnes Buzyn told AFP Sunday she would run in Griveaux's place.

"I'm going for it with the aim of winning," Buzyn, who has been leading France's response to the coronavirus outbreak, told AFP by telephone.

Macron hailed Buzyn's "courageous decision" to throw her hat in the ring for the Paris job, his office said.

The president swiftly chose Olivier Veran, an MP and doctor, to replace Buzyn at the health ministry.

- Ill-starred campaign -

Griveaux's campaign had already been in trouble before the sex tape emerged, dragged down by a rebel candidacy from fellow Macron supporter and star mathematician Cedric Villani.

Recent polls had placed the official LREM candidate third, behind incumbent Mayor Anne Hidalgo, a Socialist, and conservative candidate Rachida Dati.

Griveaux had blamed the rebel candidacy of fellow Macron supporter and star mathematician Cedric Villani for his poor showing.

The polls showed Villani, who was booted out of LREM for failing to rally behind Griveaux, running in fifth place.

- Raging against 'apathy' -

Pavlensky has a track record of causing outrage.

In 2013, he nailed his scrotum to Red Square to protest against the "apathy and political indifference" of Russian society.

Two years later, he doused the doors of the FSB secret police headquarters with petrol and set them on fire.

In October 2017, he set fire to the offices of the Bank of France on Place Bastille, site of the attack on an infamous prison at the start of the French revolution in 1789.

The activist, who has expressed support for France's "yellow vest" protest movement, was given a short jail sentence over that incident.

He is also accused of pulling a knife during a brawl at a New Year's Eve party in Paris in December.

Two guests at the party suffered minor knife wounds, according to the Mediapart investigative website.