PARIS -- The Islamic State of Iraq and Syria (ISIS) has claimed responsibility for the attack on police in Paris’ iconic Champs-Elysees shopping district Thursday night, killing one officer and seriously wounding two others before police shot and killed him.

Investigators were conducting searches early Friday in at least one eastern suburb of Paris, according to three police officials. Authorities were trying to determine whether the assailant had accomplices, anti-terrorism prosecutor Francois Molins told reporters at the scene.

The attacker emerged from a car and used an automatic weapon to shoot at officers outside a Marks & Spencer’s store at the center of the Champs-Elysees, Molins said. Two police officers and a woman tourist were wounded, he said.

The attacker had been flagged as an extremist, according to two police officials, speaking on condition of anonymity because they were not authorized to publicly discuss the investigation.

Masked police stand on top of their vehicle on the Champs Elysees Avenue after a policemen was killed and two others gravely wounded in a shooting incident in Paris, France, on Thu., April 20, 2017. Reuters

A French government spokesman says the assailant opened fire on a Paris police van and was armed with an automatic firearm akin to a “war weapon.”

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French Ministry spokesman Pierre-Henry Brandet said the police officers were “deliberately” targeted.

A video posted to Twitter and recorded by Vincent Barrano allegedly shows when the shooting happened:

Barrano told CBS News that he was in his car and heard what sounded like rapid firecrackers. Then he saw people starting to run and noticed more firecracker sounds, but much different than the first sets he heard (as if it were another gun).

French President Francois Hollande held a press conference after an emergency meeting with Prime Minister Bernard Cazeneuve.

He said the entire area is on lockdown and a full investigation will be carried out to find a motive. President Hollande says he is convinced the circumstances of the shooting points to a terrorist act.

The president said a bystander was shot and sent condolences to the families of the victims and announced there will be a national tribute on Friday as well as a security cabinet meeting.

A still image from video footage shows Police investigators inspect the car used by the attacker on the Champs-Elysees Avenue after a policemen were killed and two others gravely wounded in a shooting incident in Paris, France, on Thu., April 20, 2017. Reuters

On Thursday night, emergency vehicles blocked the wide Champs-Elysees, an avenue lined with shops and normally packed with cars and tourists that cuts across central Paris between the Arc de Triomphe and the Tuileries Gardens.

The gunfire sent scores of tourists fleeing into side streets.

A witness identified only as Ines told French television station BFM that she heard a shooting and saw a man’s body on the ground before police quickly evacuated the area where she works in a shop.

Bystanders raise their arms as police seal off the Champs Elysees avenue in Paris, France, after a fatal shooting in which a police officer was killed along with an attacker, on Thu., April 20, 2017. AP

Shortly after the shooting, President Trump said the shooting “looks like another terrorist attack” during a press conference with Italian Prime Minister Paolo Gentiloni Silveri at the White House.

“First of all our condolences to the people of France,” Mr. Trump said. “What can you say? It just never ends. We have to be strong and we have to be vigilant.”

"Our condolences from our country to the people of France" -@POTUS reacting to the attack in Paris https://t.co/bzfLoWNiGT pic.twitter.com/jFKu8OguYS — CBS Evening News (@CBSEveningNews) April 20, 2017

Subway stations in the area were closed off on Thursday night while police secured the scene.

Twitter user Massimo Cavazzini posted this video of police cars rushing to the scene:

Badi Ftaïti, a Tunisian-born mason who has spent three decades in Paris, said the attack didn’t panic him.

But the 55-year-old says visitors to the French “were running, running ... Some were crying. There were tens, maybe even hundreds of them.”

Asked whether the attack was evidence that “Paris isn’t Paris” anymore, as claimed by Mr. Trump, Ftaïti said Mr. Trump is “barking up the wrong tree.”

He says: “Paris is Paris. It’s America that’s not America.”

An armed soldier secures a side road near the Champs Elysees Avenue after a policemen was killed and two others gravely wounded in a shooting incident in Paris, France, on Thu., April 20, 2017. Reuters

The attack came three days before the first round of balloting in France’s tense presidential election. Security is high preceding the vote after police said they arrested two men Tuesday in what they described as a thwarted terror attack.

The incident recalled two recent attacks on soldiers providing security at prominent locations around Paris, one at the Louvre museum in February and one at Orly airport last month.

A police officer stands guard after a fatal shooting in which a police officer was killed along with an attacker on the Champs Elysees in Paris, France, on Thu., April 20, 2017. AP

A French television station hosting a televised event with the 11 candidates running for president briefly interrupted its broadcast to report the shootings.

Marine Le Pen, one of the candidates, tweeted out the following message: “Emotion and solidarity for our security forces, again being targeted.”

Émotion et solidarité pour nos forces de l'ordre, à nouveau prises pour cible. MLP — Marine Le Pen (@MLP_officiel) April 20, 2017

Conservative contender Francois Fillon said on France 2 television he was canceling his planned campaign stops on Friday.

Centrist candidate Emmanuel Macron offered his thoughts to the family of the dead officer.

Socialist Benoit Hamon tweeted his “full support” to police against terrorism.

The two top finishers in Sunday’s election will advance to a runoff on May 7.