A group of serving French soldiers has published a new open letter in a conservative magazine warning President Emmanuel Macron that the "survival" of France is at stake after he made "concessions" to Islamism.

The letter published in the conservative Valeurs Actuelles magazine published late on Sunday echoes the tone of a similar letter printed in the same magazine last month which also warned a civil conflict was brewing.

The previous letter, signed by a handful of officers and some 20 semi-retired generals, sparked a furor in France with the prime minister calling it an unacceptable interference and France's top general vowing those behind it would be punished.

It is not clear how many people are behind the current letter or what their ranks are. In contrast to the previous letter, it is also open to be signed by the public.

"We are not talking about extending your mandates or conquering others. We are talking about the survival of our country, the survival of your country," said the letter, which was addressed to Macron and his cabinet.

The authors described themselves as serving soldiers from the younger generation of the military, a so-called "generation of fire" that had seen active service.

"They have offered up their skin to destroy the Islamism that you have made concessions to on our soil."

They added they had also served in the security operation within France launched after a wave of attacks in 2015. They observed that for some religious communities "France means nothing but an object of sarcasm, contempt or even hatred."

It added: "If a civil war breaks out, the military will maintain order on its own soil... civil war is brewing in France and you know it perfectly well."

The letter comes in a febrile political atmosphere in France ahead of 2022 polls where Macron's main challenger is expected to be far-right leader Marine Le Pen.

Prime Minister Jean Castex had labelled the rare intervention in politics by military figures in last month's letter "an initiative against all of our republican principles, of honor and the duty of the army". 

France's armed forces chief of staff General Francois Lecointre said those who signed it will face punishments ranging from forced full retirement to disciplinary action.