The French housing estates hit by a wave of riots a year ago could once again descend into violence, an intelligence report has warned.
Buses and cars are still being set alight in French suburbs
The conditions that led to the 2005 unrest are still in place, it says.
The warning comes just days before the anniversary of the first riots, following the death of two youths in an estate north-east of Paris.
Recent weeks have seen a rise in clashes between police and youths in the capital's immigrant suburbs.
The report by the intelligence agency of the interior ministry, dated 11 October, was leaked to the Figaro newspaper.
The BBC's Jonny Dymond in Paris says the document paints a bleak picture of France's most troubled areas.
The situation, it says, is particularly tense in Clichy-sous-Bois, the suburb of Paris where the two youths died on 27 October 2005, in circumstances that remain unclear.
Some local people say they were being chased by officers at the time - which the police denies.
2005 UNREST IN FIGURES
9193 cars burnt
21 nights of riots
Source: French police
Although the area is quiet now the report said it could tip over any moment into violence.
The whole of the greater Paris region is a source of deep concern, the intelligence agency says.
It notes that any coming violence could be less spontaneous but "more structured, and targeting representatives from the last institution remaining in some neighbourhoods - the police".
In the last few weeks the number of attacks has risen sharply.
On 13 October, police responding to an emergency call in Epinay, north of Paris, were attacked by a gang waiting for them.
At the weekend, youths set fire to a bus in Grigny, south of the capital, and stoned police and firefighters as they came to the rescue.
About 9,000 cars were torched in the three weeks of unrest last year, which spread through the country's housing estates - dominated by immigrants and their French-born children.
The areas are blighted by high crime and unemployment.