Jacques Chirac called for calm today after six nights of rioting in the suburbs of Paris threatened to spread and ministers argued over the French government's response to the crisis.

A total of 34 people were arrested last night after setting fire to 15 cars and clashing with riot police in the poor, crime-ridden suburb of Aulnay-sous-Bois to the east of Paris. No one was injured.

Police have fought with protesters every night since last Thursday, when two teenagers were electrocuted after running into an electricity sub-station in the mistaken belief that they were being chased by the police. More than 150 fires have been reported, and tensions were increased after police fired tear gas into a mosque.

The battle to contain the riots, which have spread from the neighbourhood of Clichy-sous-Bois to nine other districts, has divided French opinion and M Chirac's Cabinet.

Some observers feel a degree of sympathy with the protesters, many of whom are North African immigrants who live on dilapidated estates among endemic crime and unemployment.

Nicolas Sarkozy, the Interior Minister who has been leading the government's response to the disturbances, was accused of heavy-handedness by a fellow cabinet minister yesterday after he described the rioters as "scum".

Today, M Sarkozy, who is expected to run for President in 2007, maintained his strong line, telling Le Parisien newspaper: "I talk with real words. When someone shoots at policemen, he’s not just a ’youth’, he’s a lout, full stop."

M Chirac struck a more conciliatory note in a Cabinet meeting this afternoon. "Tempers must calm down," the President told his ministers, according to his official spokesman.

"The law must be applied firmly and in a spirit of dialogue and respect," M Chirac went on. "The absence of dialogue and an escalation of a lack of respect will lead to a dangerous situation."

M Chirac said he understood the "profound frustrations" of those living in the suburbs of Paris, where unemployment routinely runs at twice the national average and police are unwilling patrol the streets, but said that grievances must be resolved peacefully.

Charles Bremner, Paris correspondent for The Times, said that M Chirac's comments were "a slap in the face to Sarkozy, who has a habit of going too far in these situations."

As a measure of the crisis, Prime Minister Dominique de Villepin has delayed a three-day visit to Canada indefinitely and M Sarkozy has cancelled a visit to Pakistan and Afghanistan that had been planned for next week.

Looking ahead to this evening, Claude Dilain, the Mayor of Clichy-sous-Bois, the place at the centre of the rioting, said that even if the neighbourhood is calm tonight, it will not be "a victory, because we all have the feeling that this calm could be precarious."

"If French society accepts that there are tinderboxes within its borders, it can’t be surprised when they explode," he said.

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