A 36-year-old man has been arrested and placed in psychiatric care after he smeared a glass screen encasing the Mona Lisa with cake, prosecutors said Monday, in a purported protest against artists not focusing enough on "the planet."

Officials at the Louvre Museum in Paris, where the enigmatic portrait holds pride of place, declined to comment on the bizarre incident on Sunday, which was captured on several phones and circulated widely on social media.

The treasured work by Leonardo da Vinci, which has been the target of vandalism attempts in the past, was unharmed thanks to its bulletproof glass case.

A Twitter user identified as Lukeee posted a video showing a museum employee wiping a mess off the glass and another showing a man dressed in white being escorted away by security guards.

"A man dressed as an old lady jumps out of a wheelchair and attempted to smash the bulletproof glass of the Mona Lisa. Then proceeds to smear cake on the glass and throws roses everywhere, all before being tackled by security," Lukeee wrote.

Speaking French, the man says: "There are people who are destroying the Earth... All artists, think about the Earth. That's why I did this. Think of the planet."

No image have emerged showing the actual incident.

An inquiry into "an attempt to vandalize a cultural work" has been opened, the Paris prosecutor's office said.

The Mona Lisa has been behind glass since a Bolivian man threw a rock at the painting in December 1956, damaging her left elbow. In 2005, it was placed in a reinforced case that also controls temperature and humidity.

In 2009, a Russian woman threw an empty teacup at the painting, which slightly scratched the case.

The Louvre is the largest museum in the world, housing hundreds of thousands of works that attracted some 10 million visitors a year before the Covid-19 pandemic.