France's far-right National Front has announced it plans to sue Madonna over a video at the US pop star's concert in France showing party leader Marine Le Pen with a swastika on her forehead.
"We cannot accept such an odious comparison," National Front vice-president Florian Philippot said, adding that the legal action would be filed this week.
The video, which served as a backdrop for Madonna's performance of the song Nobody Knows Me, flashed a picture of Le Pen's forehead superimposed with a swastika, followed by an image resembling Nazi leader Adolf Hitler.
There was an audible gasp from the audience at the Stade de France on Saturday when the image of Le Pen appeared briefly on a giant screen in a video clip which also showed Madonna's face merging with a number of public figures including Pope Benedict XVI and toppled Egyptian president Hosni Mubarak.
"Projecting such an image of Marine Le Pen with a swastika implies that she is a Nazi," National Front lawyer Wallerand de Saint-Just told AFP, adding that the civil complaint for insult would be lodged with a court this week.
Tour promoter LiveNation declined to comment on the National Front action against the queen of pop, who has been no stranger to controversy during her long career.
"This is just another provocation in Madonna's world tour so that people will talk about her," Philippot charged, claiming that the stadium was "far from full" for Madonna's gig and that the tour was a "fiasco".
"Marine Le Pen will defend not only her own honour but her supporters and the millions of National Front voters."
Le Pen, a French presidential candidate, had already warned the US superstar in June that she was mulling legal action after the video was shown at Tel Aviv gig in May when Madonna, 53, kicked off her world tour.
"(When) old singers want to get people to talk about them, it's understandable that they do such extreme things," the 43-year-old Le Pen said at the time.
SOS Racisme however said it supported Madonna, paying tribute to her "resolutely anti-racist" stance. "She made clear last night that the fight against discrimination is a fundamental battle."
About 70,000 people were at the Stade de France to watch the "Material Girl" perform on Saturday night, the latest concert in her "MDNA" tour which covers about 30 countries in the Middle East, Europe and the Americas and will wrap up in Australia in 2013.
Madonna will next appear in France in Nice on August 21.
In 1987, Madonna caused a stir when she threw her panties into the crowd at a concert where then president Jacques Chirac was in attendance.
On her latest world tour, she made headlines when she flashed a nipple at a gig in Turkey's largest city of Istanbul last month.
Le Pen, the daughter of National Front founder Jean-Marie Le Pen, won 18 per cent in the first round of the presidential election in April.
But she lost her bid to win a seat in legislative elections last month although the party - which wants to ditch the euro and battles against what Le Pen calls the "Islamisation" of France - returned to parliament for the first time since 1998.