PARIS (AFP) - Facebook admitted on Sunday (March 18) making a mistake after it banned an advert featuring French artist Eugene Delacroix's famous work, "Liberty Leading the People," because it depicts a bare-breasted woman.

The 19th-century masterpiece was featured in an online campaign for a play showing in Paris when it was blocked on the social networking site this week, the play's director Jocelyn Fiorina said.

"A quarter of an hour after the advert was launched, it was blocked, with the company telling us we cannot show nudity," Fiorina said.

He then posted a new advert with the same painting with the woman's breasts covered with a banner saying "censored by Facebook", which was not banned.

Delacroix's subject who brandishes a French flag in the painting is not just any woman - she's Marianne, a national symbol of the French Republic.

Fiorina had already tried twice before in June without success to use the painting, which once featured on a franc bank note, in publicity for the theatre.

But by Sunday the US social media giant had a change of heart and apologised "for this error".

"The work 'Liberty Leading the People' rightly has its place on Facebook... We have immediately informed the user that his sponsored publicity is henceforth approved," Facebook manager in Paris Elodie Larcis said in a statement.

"In order to protect the integrity of our service, we verify millions of publicity images each week and sometimes we make mistakes," she said.

With over one billion users, Facebook is often challenged over its authorisation or not of content on its site.

On Thursday, a Paris court threw out a case brought by a French teacher who wanted to sue Facebook over his claims that his page was censored when he posted a nude painting by Gustave Courbet.

The court however added that Facebook had made "a mistake" in not specifying to the user the reasons for its move.