A number of serving defence force members signed the dramatically-worded letter published last week in the right-wing Valeurs Actuelles magazine, which warned that "laxist" policies would result in chaos requiring "the intervention of our comrades on active duty in a perilous mission of protection of our civilisational values".

Failure to act against the "suburban hordes" -- a reference to residents of the mainly immigrant tower blocks that ring French cities -- and other unnamed groups who "scorn our country, its traditions and its culture" will lead to "civil war" and deaths "in the thousands", the signatories warned.

The government and left-wing parties strongly condemned the letter, which was published on the 60th anniversary of a failed coup d'etat by generals opposed to France granting independence to Algeria.

"These are unacceptable actions," Defence Minister Florence Parly said Monday, adding that serving military members, who in signing the letter flouted a law requiring them to remain politically neutral, would be punished.

"There will be consequences, naturally," Parly told France Info radio, adding that she had instructed the army chief of staff to discipline them.

The letter comes as candidates begin jockeying for position on immigration, security and other hot-button issues in the run-up to the 2022 presidential election.

An Ifop poll published in the Journal du Dimanche weekly showed security and the fight against terrorism among voters' top priorities after a new wave of jihadist attacks, including the October 2020 beheading of a schoolteacher who showed his pupils cartoons of the Prophet Mohammed.

Far-right leader Marine Le Pen, whom polls show likely to face off against Macron in the final round of the race for president in a re-run of the 2017 race, told the retired generals she shared their sentiments and invited them to back her campaign.

"I invite you to join us in taking part in the coming battle, which is the battle of France," she wrote in a response to the letter published in Valeurs Actuelles.

Le Pen was widely criticised by her opponents on both the left and right for her overtures to the soldiers behind what the left-wing daily Liberation described as a "call to sedition".

On Tuesday, she told France Info that while she shared their diagnosis of a country afflicted by "lawless areas, crime, self-hatred and our leaders rejection of patriotism" she agreed that "these problems can only be solved by politics."

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