Police raids are under way in Paris after an armed attacker shot three police officers on the Champs-Elysees.
France's anti-terrorism prosecutor Francois Molins confirmed searches were being carried out in the capital and said that investigators had already verified the identity of the gunman but were trying to determine whether he had accomplices.
He said: "The identity of the attacker is known and has been checked. I will not give it because investigations with raids are ongoing."
Officials confirmed that at least one location in the eastern Paris suburbs was being searched early Friday.
The so-called Islamic State has said it was behind the Paris shooting that left at least one policeman dead and two others wounded.
The claim was made through its affiliated Amaq agency.
It is not clear whether they are claiming to have directed the attack or whether it was simply carried out in their name.
The French president said he was convinced that the shooting of police officers in Paris was a terror-related attack.
Francois Hollande also said he would call an security cabinet meeting at 8am on Friday morning in a brief speech.
He said security forces would be on high alert during the forthcoming presidential election.
"We shall be of the utmost vigilance, especially in relation to the election," he said.
French presidential candidate Francois Fillon has cancelled campaign events scheduled for Friday following the shooting in Paris - and called for the election campaign to be suspended altogether.
The shooting on the Champs-Élysées, which left one police officer dead and two seriously injured, took place just days before the first round of voting in the election on Sunday.
According to aides who spoke to Agence France-Presse, National Front candidate Marine Le Pen has also cancelled her planned events.
A police officer has been killed and two others wounded in a shooting in the centre of Paris - here's what we know so far.Read the full story ›
A gunman who opened fire on police officers in Paris used a "war weapon" to carry out his attack, a French government spokesman said.
The attacker was killed after police returned fire on the Avenue des Champs-Élysées on Thursday evening.
It follows reports from eyewitnesses who claimed the attacker used a Kalashnikov-style gun.
An automatic weapon was used against police, a weapon of war. adding that the "terrorist threat" in the country remained high.
The shooting started shortly after 9pm, when a car stopped alongside a stationary police car.
A man immediately got out and opened fire on the police car, fatally
wounding a police officer. He also wounded a second one, it would seem very seriously.
A second police officer has not died, but two remain in a critical condition in hospital after being injured in a shooting in Paris, an Interior Ministry spokesman has said.
Speaking at the scene of the attack, he said one officer had been killed and two others had been taken to hospital with serious injuries.
He added that they believe there was just the one gunman, who was killed by police - but he said he cannot rule out that the man may have had accomplices.
The spokesman also emphasised that they did not yet know the motive of the attack.
French Prime Minister Bernard Cazeneuve has paid tribute to the officers killed and injured in a shooting in central Paris.
Hommage au policier tué sur les Champs-Elysées ce soir, pensées à sa famille. Solidarité avec ses collègues blessés et leurs proches.
Several metro station in central Paris have been closed as the area goes into lockdown following a shooting that has killed at least one police officer.
Paris police have warned people to avoid the Champs-Elysses area following the attack.
A second policeman has died after being injured in a shooting in central Paris, according to reports.