PARIS (AFP) - French far-right leader Marine Le Pen on Thursday (Dec 17) withdrew a photograph of the decapitated body of US journalist James Foley from her Twitter account after his parents accused her of using it for political gain.

"I did not know it was a photograph of James Foley. It can be accessed by anyone on Google. I learned this morning that his family has asked for it to be removed and of course I took it down immediately," said Le Pen who posted the image after a journalist compared her National Front (FN) party to the Islamic State group which killed Foley.

She had been under investigation Wednesday (Dec 16) after tweeting graphic images of Islamic State atrocities, among James Foley's photo.

The prosecutor's office in the western Paris suburb of Nanterre told AFP it had launched an investigation into "the dissemination of violent images" over the National Front (FN) leader's series of shock tweets.

The images were tweeted with the caption "This is Daesh" (an Arabic acronym for the Islamic State group) and showed Foley's bloodied body with his decapitated head on his torso, a man on fire in a cage, and a victim being driven over by a tank.

Foley's bereaved parents John and Diane said they wanted the images removed immediately, accusing Le Pen in a statement of using the "shamefully uncensored" image to her own political ends.

"We are deeply disturbed by the unsolicited use of Jim for Le Pen's political gain and hope that the picture of our son, along with the two other graphic photographs, are taken down immediately," they said.

Foley, a freelance journalist, was captured in Syria in 2012 and beheaded in August 2014.

Le Pen, who has over 830,000 Twitter followers, addressed the tweets to BFM TV journalist Jean-Jacques Bourdin, whom she accused of likening her party to the militant group.

Mainstream media largely refrain from showing any potentially disturbing or gruesome photos from such incidents.

French Prime Minister Manuel Valls described the photos as "monstrous".

"Madame Le Pen: inflaming public debate, political and moral failing, non-respect for victims," he wrote on his Twitter account.

Interior Minister Bernard Cazeneuve alerted the police to look into the tweets "as they do every time these photos are published".

The photos are "Daesh propaganda and are a disgrace, an abomination and an absolute insult to all victims of... Daesh," said Cazeneuve.

Le Pen was reacting to comments by Bourdin, whom she accused of drawing parallels between her party and the ISIS militant group in an "unacceptable bungle".

Bourdin, during his morning show known for combative one-on-one interviews, suggested there were "links" between FN and ISIS.

In later remarks Bourdin dismissed Le Pen's reaction as "hysterical".

"At no point did I say the FN was like Daesh," he insisted.

FN lawmaker Gilbert Collard also tweeted a picture of an ISIS victim, albeit one that was far less graphic than those posted by Le Pen.

"We are only showing the hate-filled ignominy of those who (compare) us with killers," Collard, who was also placed under investigation, said by way of explanation.

Le Pen's FN scored a record number of votes in regional elections on Sunday, boosted by concerns over the migrant crisis and terrorism, though the party failed to win control of any regions.

In the wake of the November 13 attacks in Paris that left 130 people dead, Le Pen warned that if IS was not conquered "Islamist totalitarianism will take power in our country".