Thousands of extra police moved into the Paris suburbs late on Friday amid new attacks on public buses, as the restive communities marked the anniversary of the death of two teenagers a year ago which sparked riots and France's most serious social crisis in decades.
"Four thousand police have been made available and will reinforce local personnel in order to ensure the security of citizens in sensitive districts," a national police headquarters spokesman said.
In the town of Blanc-Mesnil, in the violence-prone Seine Saint Denis region, police said on Friday evening masked people attacked two public buses, setting them alight, bringing to six the number of such incidents in France since Wednesday.
The drivers and passengers were let out of the buses before the attacks took place and were unhurt, RATP transportation company officials said.
The mayor of Blanc-Mesnil Daniel Feurtet quickly condemned the attacks but added they "were nothing compared with what we saw in November 2005".
Earlier on Friday, more than 1,000 people paid tribute in a peaceful, silent march past the spot where the two teens died in Clichy-sous-Bois, the poor north-east Paris suburb that erupted in riots on October 27, 2005.
"Once again, France and the world are watching us," the mayor of Clichy Claude Dilain told the crowd. "We need the calm, dignity and courage that are visible here to prevail. Let us show them who we really are."
Many of the marchers wore white T-shirts printed with the words "Zyed and Bouna, Dead for nothing."
Zyed Benna, 17, and Bouna Traore, 15, both from immigrant families of African descent, were electrocuted as they hid from a police patrol in a power sub-station.
Riots broke out in Clichy that night, quickly spreading to dozens of
immigrant-populated suburbs in the Paris region and other French cities.
Night after night for three weeks, youth gangs clashed with police, torching more than 10,000 cars and firebombing 300 buildings in around 275 towns, until order was officially restored on November 17.
With the approach of the anniversary, police and local mayors have warned that the conditions that led to the riots remain firmly in place in the poor out-of-town neighbourhoods, plagued by unemployment of 30 to 40 percent.
France's tough-talking Interior Minister Nicolas Sarkozy vowed on Thursday following several bus attacks the day before that the government would mobilise all the forces at its disposal for the security of public transport users.
On Friday, Sarkozy told reporters in southern France that "there is no anniversary" to celebrate -- saying his prime concern was for ordinary people "who do not smash things up (but) who count too".
Last year's riots -- which led the government to declare a state of emergency, a measure not enacted since the Algerian war half a century earlier -- cast an unforgiving spotlight on France's trouble in integrating its Arab-origin and black communities.
Badly shaken by the crisis, the government promised measures such as an extra 100 million euros (125 million dollars) for local associations, bigger training schemes and a crackdown on racial discrimination for jobs.
But a chorus of voices has warned of the inertia that dogs French policy towards the "banlieues", as the suburbs are known.
With six months to go to France's presidential election, the festering situation is certain to be a main campaign theme.
The opposition Socialist Party accuses Sarkozy, the centre-right presidential frontrunner, of being part of the problem because of a tough line on law and order that has made him a hate figure in the "banlieues".
Sarkozy argues that left-wing welfare policies are at the root of the crisis -- and that a liberalised economy combined with positive discrimination is the only way to provide jobs and hope.