One policeman has been killed and two others injured in a shooting in central Paris, police and the interior ministry said.
The shooting took place on the Champs-Elysees just days ahead of France's presidential election.
The assailant was killed by security forces, and a witness told Reuters one man got out of a car at the scene and began shooting with a machine gun. A police source said more shots had been fired at another location nearby.
President Francois Hollande said he was convinced the attack was "terrorist-related", and the so-called Islamic State has clamed responsibility for the attack.
According to French media, the killer was known to the security services and had talked of wanting to kill police officers.
No motive has yet been reported, and a French interior ministry spokesman said it was too early to say, but it was clear the police officers had been targeted deliberately.
The French prosecutors' office said counter-terrorism had opened an inquiry, but police sources said the attack could have been an attempt at an armed robbery.
The incident comes ahead of France's presidential election on Sunday - the most tightly-contested presidential election in living memory.
Earlier this week, two men were arrested in Marseille whom police said had been planning an attack ahead of the election.