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PARIS -- A man who shot a Parisian police officer to death on the Champs-Elysees on Thursday night was known to French security services for radical Islamist activities, a source close to the investigation said.

The suspect, who was shot dead by French police, was the subject of a "Fiche S" surveillance file and was on the radar of the French domestic security service DGSI, the source said.

The source said French investigators now believe this was in all likelihood a terrorist attack. They believe there was just one attacker, and the danger is likely over, the source said.

ISIS issued a statement saying an Islamic State "fighter" carried out the attack. The ISIS claim comes via a statement released by the group's media wing, Amaq.

The statement said the attacker is a Belgian national and cited "security sources."

French President Francois Hollande said anti-terrorist forces are leading the investigation.

"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.

The shooting happened about 9 p.m. local time when a car stopped at 102 Champs-Elysees in front of a police van, Interior Ministry spokesman Pierre Henry Brandet said.

A man emerged from the car and opened fire on the van with an "automatic weapon," killing one officer instantly, he said.

The man "then ran away, managing to shoot and wound two other policemen. Other policemen engaged and shot and killed the attacker," Brandet said.

Hollande also said a woman passer-by was wounded in the shooting.

Police union spokesman Yves Lefebvre from Unite SGP Police said officers were raiding the suspect's residence in Chelles, Seine-et-Marne. He said police are operating under the assumption that there might be accomplices.

The shooting shut down the famed Champs-Elysees, one of Paris' top tourist attractions and home to the iconic Arc de Triomphe monument. The avenue was clear of residents and tourists but teeming with security officers Thursday night.

It comes three days before French voters start elections for a new president. Candidates went ahead with a debate Thursday night.

France has been in a state of emergency since the 2015 Paris attacks, which left 130 people dead. Parliament voted in December to extend the extraordinary provisions to ensure the protection of upcoming presidential and general elections.

Security has been tight because of the vote. Just two days ago French authorities arrested two men in Marseille who were allegedly planning an attack in a run-up to the election.

At least three underground train stations of the Paris Metro -- the Champs-Elysees-Clemenceau, George V and F. Roosevelt stations -- have been "closed off" near the site of the police operation on the Champs-Elysees in Paris, BFMTV reported.