French prosecutors on Monday opened a probe into allegations of racism after a right-wing magazine published images depicting a black woman MP as a slave, prompting a nationwide outcry.

The Valeurs Actuelles weekly unleased a storm of controversy with the publication of the images of left-wing MP Daniele Obono with a chain fixed to an iron collar around her neck.

A preliminary investigation has now been opened into "attacks of a racist nature", Paris prosecutor Remy Heitz said in a statement.

The French presidency said at the weekend President Emmanuel Macron had called Obono, who is from the far-left party France Unbowed, and "expressed his clear condemnation of any form of racism".

Prime Minister Jean Castex said it was a "revolting publication that calls for clear condemnation" and told Obono that she had the government's backing.

Daniele Obono sits in the French parliament for far-left party France Unbowed
Daniele Obono sits in the French parliament for far-left party France Unbowed AFP / Ludovic Marin

Obono tweeted: "The extreme right -- odious, stupid and cruel. In short, being itself."

Valeurs Actuelles, which is seen by commentators as sympathetic to the far-right, however denied the image was racist.

It said the seven page story concerning Obono -- which it called an "imaginary fiction" -- was "a work of fiction... but never nasty."

France has witnessed several protests in June and July against racial injustice as well as colonial and police brutality, inspired by the Black Lives Matter movement and George Floyd's death under the knee of a police officer in the United States.

Centrist Macron raised eyebrows when he gave an interview to Valeurs Actuelles last year and praised it as a "good magazine".

While he has pledged to root out racism, he also said France will not take down statues of figures linked to the colonial era or the slave trade, as has happened in other countries recently.