A woman was seized by security guards after using marker pen to deface one of the most famous paintings by Eugene Delacroix at an exhibition in northern France.
The woman, 28, wrote an inscription in marker on the French Romantic artist's most recognisable painting "La Liberté guidant le peuple" or "Liberty Leading the People".
She was intercepted by a guard and another visitor before being handed over to police.
A statement from the Louvre-Lens, an extension of the famous Paris-based Louvre which only opened last December, where the incident took place, said the painting "could be easily cleaned" and is being examined by a restorer.
A report in Le Figaro newspaper claims the woman wrote "AE911" near the bottom of the canvas which is alleged by unnamed sources quoted in the French press to be a reference to a 9/11 conspiracy theory.
Before France switched to the Euro Delacroix's painting featured on the 100 franc banknote.
"Liberty Leading the People" is on loan to Louvre-Lens for a year. The work, which depicts a bare-chested woman holding the French flag during the July Revolution of 1830, is thought to have inspired the Statue of Liberty.
It is the latest in a series of high profile defacements of public art. In December Wlodzimierz Umaniec, 26, was jailed for two years for vandalising a painting by Mark Rothko worth £9 million in the name of his yellowist movement at the Tate Modern gallery, London.