The Champs Elysees, one of the most popular sites in Paris, was shut down on Thursday evening after a gunman opened fire on officers in the famous shopping district. He was convicted in that attack and had a criminal record because of involvement in violent robberies, the source said. Belgian authorities said they had no information about the suspect.
The Islamic State group's claim of responsibility just a few hours after the attack came unusually swiftly for the extremist group, which has been losing territory in Iraq and Syria.
CNN could not independently confirm that claim.
Paris Prosecutor Francois Molins said he will reveal the shooter's identity on Friday at a news conference.
He said police were securing the area but there is "no other police operation under way" there.
"The people who were present have been evacuated and we are convinced that the leads which point us to this case, and which will allow us to uncover the truth, are of a terrorist nature", he said.
One officer was killed and two police officers were seriously wounded when the attacker emerged from a vehicle and used an automatic weapon to shoot at officers outside a Marks & Spencer's department store at the center of the Champs-Elysees, anti-terrorism prosecutor Francois Molins said.
A French police union tweeted that an "individual in a vehicle opened fire at a police auto stopped at a red light, killing one policeman". The man "then ran away, managing to shoot and wound two other policemen".
Police said the attacker was shot dead by an officer or officers.
The slain officer was 30 years old, Molin said. "He also wounded a second one, it would seem very seriously", he said.
A police officer stands guard after a fatal shooting on the Champs Elysees in Paris, France, Thursday, April 20, 2017.
A second suspect thought to be involved in the incident on the Champs Elysees shopping boulevard just days ahead of France's presidential election was still on the loose. Candidates went ahead with a debate Thursday night.
Security forces are more widespread in Paris since deadly Islamic extremist attacks in recent years, and France remains under a state of emergency.
Security has been tight because of the vote.
Helicopters were seen flying low over central Paris, and the Champs Elysees, one of the world's most prestigious boulevards, had been closed off.
Trump: 'What can you say?' He looked around, but couldn't identify where the shots were coming from.
"But at this stage I'm advised that the French prosecutor is on the scene and they'll obviously be making further announcements as they investigate the crime", he told the Seven Network on Friday.
The CNN Paris bureau is on this street and staffers reported hearing a dozen shots.