A prosecutor has asked for the acquittal of two French police officers on trial over alleged conduct blamed for igniting a wave of riots in heavily immigrant suburbs in 2005.

The officers are accused of deliberately failing to rescue two teenagers of foreign origin killed in a power station, deaths that sparked outrage in the decaying housing projects ringing Paris.

Three weeks of urban riots ensued, triggering a state of emergency declaration.

On Thursday, prosecutor Delphine Dewailly said she didn't believe the officers saw Bouna Traore, 15, and Zyed Benna, 17, enter the station where they were struck down by 20,000 volt electric shocks.

French judges, who make the final ruling, often follow the prosecution's request but not always.

There has been concern that an acquittal could prompt fresh riots.