PARIS (AFP) - French far-right leader Marine Le Pen voiced outrage on Thursday (Sept 20) after being ordered to undergo psychiatric tests for having posted pictures of atrocities committed by the Islamic State in Iraq and Syria (ISIS) group on Twitter.

Ms Le Pen shared the gruesome images in December 2015, a few weeks after ISIS militants killed 130 people in attacks in Paris, sparking widespread condemnation in France.

The 50-year-old leader of the National Rally (formerly National Front), who lost to Mr Emmanuel Macron in last year's presidential vote, was stripped of her parliamentary immunity over the pictures and charged with circulating messages that "incite terrorism or pornography or seriously harm human dignity".

On Thursday, she tweeted copies of a court order ordering her to undergo psychiatric evaluation.

Dated Sept 11, it calls for the tests to be carried out "as soon as possible" to establish whether she "is capable of understanding remarks and answering questions".

"It's crazy," fumed Ms Le Pen, herself a trained lawyer. "This regime is really starting to be frightening," she tweeted, suggesting that the case was part of a government plot to discredit her.

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"I thought I had been through it all: well, no! For having condemned Daesh (ISIS) horrors in tweets, the 'justice system' is putting me through psychiatric tests! Just how far will they go?" she asked.

Ms Le Pen had shared the images in response to a French journalist who drew a comparison between ISIS and her party.

One of the pictures showed the body of Mr James Foley, an American journalist beheaded by the Sunni extremists.

Another showed a man in an orange jumpsuit being run over by a tank, and a third showed a Jordanian pilot being burned alive in a cage.

"Daesh is this!" Ms Le Pen wrote in a caption. Daesh is an Arabic acronym for ISIS.

She later deleted the picture of Mr Foley after a request from his family, saying she had been unaware of his identity.

If convicted, she faces up to three years in prison and a fine of €75,000 (S$120,000).

Ms Le Pen has denounced the case against her, which falls under a law punishing violent images that can be viewed by a minor, as a violation of her freedom of expression.

Another National Rally lawmaker, lawyer Gilbert Collard, has also been charged for tweeting pictures of ISIS atrocities.