A police officer was gunned down in the heart of this capital on Thursday, just three days before French voters will cast ballots in the first round of the presidential election.
Islamic State rushed to claim responsibility for the attack, which left the policeman and the assailant dead and three others wounded, including a civilian.
Police have confirmed the identity of the gunman, but are withholding his name to allow time to determine whether he had any accomplices, Paris chief prosecutor François Molins said at the crime scene.
Investigators have already searched the shooter's residence in suburban Paris, Efe news agency reported.
IS said the assault was the work of one of its "soldiers," a Belgian national identified only by the pseudonym Abu Yusuf al-Baljiki.
French President François Hollande said he was convinced the shooting was an act of a "terrorist character."
"We have a great determination to battle terrorism here and everywhere our forces are engaged," the head of state said in a televised address.
"With regard to the security forces, the nation's support is total," Hollande said, adding that the government will organize a tribute to the slain policeman.
Authorities will remain on the highest alert, especially for possible threats to the election, he said.
Hollande said he convened a meeting of France's defense council for Friday morning.
The incident on the Champs-Elysees, Paris' iconic main avenue, occurred shortly before 9 pm, interior ministry spokesman Pierre-Henry Brandet said.
A car pulled up next to a police vehicle and a man emerged and opened fire with an automatic weapon, the spokesman said.
"On the face of it, the officers were deliberately targeted," Brandet said.
Evidence and witness statements indicate that the attack was carried out by one man, Brandet said.
Paris police ordered the immediate evacuation of the Champs-Elysees and suspension of service at nearby metro stations.
France has been under a state of emergency since November 2015, when more than 130 people were killed in a single night by coordinated terrorist attacks in Paris.
Several of the candidates vying in Sunday's presidential ballot issued statements of sympathy for the victims and their families, and some referred to the shooting an act of terrorism.
Two presidential hopefuls canceled rallies scheduled for Friday.
US President Donald Trump, in comments prior to Hollande's televised address, said that the violence in Paris "looks like another terrorist attack."
"It never ends," he said during a joint press conference in Washington with the visiting Italian prime minister, offering condolences to the French people.
(With IANS inputs)