A controversial painting by Swiss artist Miriam Cahn on display at a Paris exhibition was vandalised with spray paint Sunday, the Palais de Tokyo contemporary art museum said.
The painting entitled "Fuck abstraction!", on display since mid-February, shows a person with their hands tied behind their back being forced to perform oral sex on a faceless, powerful man.
Several children's rights groups had denounced the painting as child pornography, calling for it be withdrawn.
But their bid to have it removed was rejected in the French courts.
On Sunday, a man "deliberately degraded" the work "by projecting paint" in purple, the museum told AFP.
The man, described as elderly, according to a source close to the case, was "unhappy with the sexual portrayal of a child and an adult presented in the painting" but was not affiliated with an activist group.
He "was immediately apprehended by security agents... and taken away by police", the museum said, adding it would file a complaint for damage to property and obstruction of freedom of expression.
"We regret the extreme consequences of this controversy," said Guillaume Desanges, president of the Palais de Tokyo, which aims to "support art... with enthusiasm, awareness and responsibility toward all audiences"
"In agreement with the artist, the Palais de Tokyo will continue to present the painting and the exposition," which has attracted 80,000 visitors, "with traces of the damage until the end of the season, May 14," it said in a statement.
France's highest administrative court, the Conseil d'Etat, in April dismissed a legal bid to have the painting take down.
Given that the painting was on show in an art gallery "accompanied by detailed contextual information, (it) does not seriously or clearly unlawfully harm the best interests of the child or the dignity of the human person", it ruled.
The artist herself hit back at criticism of the work, in a statement issued by the museum in March.
"They are not children," Cahn insisted. "This painting deals with the way in which sexuality is used as a weapon of war, as a crime against humanity," she added.