Sarkozy is expected to install a new government prefect in charge of security in the region Friday, after riots broke out following the death of a local man fleeing police who suspected him of holding up a casino.

Shots were fired at police in the high-rise suburb of Villeneuve, prompting the government to send in reinforcements and to arrest some 20 people on charges ranging from attempted murder to illegal possession of firearms.

Weekly magazine Le Point reported that many of the 45 police officers in the anti-crime unit involved in the shooting had received death threats, prompting some to request sick leave or a transfer.

"These threats are credible and have been confirmed by intelligence we have received. There are contracts on the heads of some officers," Daniel Chomette, an official of the police union told Reuters.

Prime Minister Francois Fillon said the security measures were aimed at protecting the families of the police officers and not necessarily the officers themselves.

"We are dealing with extremely dangerous people, extremely violent, and therefore we're going to have to respond with great determination," Fillon said in an interview with Europe 1 radio.

"We are placing the families of those who are threatened in shelters while doing all we can to find the perpetrators of these threats," he added.

Unrest in areas on the outskirts of French cities has been a headache for Sarkozy, who came to office pledging to crack down on riots and civil disorder but has failed to reduce violent crime despite harsh rhetoric.