Chief of the defence staff General Fabien Mandon said in a speech to local mayors on Tuesday that, while France has the economic and demographic power to defeat Moscow, it lacked the "spirit" in society to stand up to the menace.

Russia and Ukraine have been at war since Moscow in February 2022 launched the full-scale invasion of its neighbour. European powers, including France, have backed Ukraine with increasing supplies of weapons but have always insisted they are not directly involved in the conflict.

"We have all the knowledge, all the economic and demographic strength to deter the Moscow regime from trying its luck by going further," said Mandon.

"What we lack, and this is where you have a major role to play, is the strength of spirit to accept suffering in order to protect who we are," he told the mayors.

"If our country falters because it is not prepared to accept -- let's be honest -- to lose its children, to suffer economically because defence production will take precedence, then we are at risk," he added.

French officials including President Emmanuel Macron have repeatedly warned that Russia risks seeking to push further if the invasion of Ukraine succeeds.

Authorities have tried to prepare the minds of the French for a war or crisis that would force them to make sacrifices, but the message is struggling to make inroads among a polarised population that feels far from the frontline and protected by a nuclear deterrent.

"It's a NO! 51,000 war memorials in our towns and villages are not enough?," said French Communist party leader Fabien Roussel, referring to the number of memorials nationwide to those who fell in war.

"Yes to national defence, but no to unbearable warmongering rhetoric!", he wrote on X.

Louis Aliot, deputy leader of the far-right National Rally said: "One must be prepared to die for one's country... but the war being waged must be just, or understood, or the necessity must dictate that the very survival of the nation is at stake... I don't think there are many French people who are ready to go and die for Ukraine."

"It's shocking," said Christian Estrosi, the mayor of Nice and a member of the centre-right Horizons party which is part of Macron's ruling coalition.

"Is it the role of the chief of staff of the army to worry the country in this way? It's an act of weakness," he told CNews.