French Prime Minister Bernard Cazeneuve hit back Monday at conservative presidential candidate Francois Fillon, accusing him of being "irresponsible" for saying the race was taking place in a climate of "near-civil war."

"For an eminent senior politician to use the term 'near-civil war' when they are perfectly well aware of the level of mobilization of the security forces in our country is quite simply irresponsible," Cazeneuve told journalists.

Fillon had Sunday accused the Socialist government of "failing to ensure the conditions for a calm democratic exercise," pointing to riots in the north-western city of Nantes Saturday ahead of a speech by far-right candidate Marine Le Pen.

Fillon also referred to weeks of disturbances in the suburbs of Paris after a policeman allegedly sodomized a young black man with his baton.

Cazeneuve suggested that Fillon was trying to distract attention from his own legal troubles, which Friday saw prosecutors refer claims that he gave his wife a lucrative fake job as his parliamentary assistant to investigating judges.

"I can understand that certain candidates are tempted to hide the difficulties of their campaigns behind polemics," the premier said.

The dispute came as opinion polls published on Sunday showed Fillon slipping back into third place, which would see him knocked out in the first round of polling on April 23.

The polls for Le Figaro and France 2 showed Le Pen in first place on 27 per cent of the vote, with centrist Emmanuel Macron on 25 per cent, pulling clear of Fillon by five to six percentage points.