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.
French police arrive at the house of the gunman killed in a shootout with police on the Champs Elysees Avenue, in the Paris suburb of Chelles April 21, 2017.
One police officer was killed and two colleagues seriously wounded when the attacker emerged from a auto and used an automatic weapon to shoot at officers outside a Marks & Spencer store at the centre of the Champs-Elysees, anti-terrorism prosecutor Francois Molins said. He shot two officers in 2001 after being stopped by a police, according to the source.
France has lived under a state of emergency declared following a terrorist attack in November 2015 that left 130 dead.
More than 50,000 police and gendarmes are mobilized to protect Sunday's first-round vote in the two-stage election, with an additional 7,000 soldiers also on patrol.
"Barbarity and cowardice struck Paris last night", the prime minister said, appealing for national unity and for people "not to succumb to fear".
He was identified as Karim Cheurfi, 39, a Paris resident, according to a representative of the Paris prosecutor's office. "It just never ends".
The Islamic State said the attack was carried out by "Abu Yousuf al-Baljiki" (the Belgian).
The attack unfolded on the famed Champs-Elysees around 9 p.m. local time (3 p.m. ET) when a auto stopped in front of a police van, according to French Interior Ministry spokesman Pierre Henry Brandet.
Police later found a pump-action shotgun, knives and a Quran in his vehicle, while a handwritten note praising IS was recovered from near the dead assailant, police sources told local media. Cheurfi's identity was confirmed from his fingerprints.
French prosecutors opened a terrorism investigation into the attack.
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None of the candidates immediately commented.
Fillon, Le Pen and independent centrist Emmanuel Macron canceled planned campaign events after the shooting.
The attack brought back the recurrent campaign theme of France's fight against Islamic extremism, one of the mainstays of the anti-immigration platform of far-right leader Marine Le Pen and also, to a lesser extent, of Fillon. Cazeneuve, the Socialist prime minister, accused the National Front leader of seeking to make political hay from the assault. "This concert is to celebrate life, to say no to terrorists". A truck ploughed into people in Nice on Bastille Day past year killing more than 80 people while coordinated attacks across Paris including the Bataclan concert hall claimed about 130 lives in November 2015. She has promised to close French borders permanently, to lead France out of the European Union and off the Euro, to rescind all free-trade agreements, and to ban Islamic veils in public.
Fillon said that if elected, his foreign policy priority would be the destruction of ISIS. "The people of France will not take much more of this", he added. Delivery trucks did their early morning rounds. Everything would have seemed normal if not for a row of TV trucks parked along the boulevard that is a must-visit for tourists.
Cheurfi was fatally shot trying to flee the scene of the shooting on the Champs-Elysees Thursday, in which what French President Francois Hollande has called a terrorist attack.
Macron said he canceled campaign stops out of a sense of "decency" and to allow police to concentrate resources on the investigation.
People on the French security services' watch list for radicalization should also be expelled from France and have their French citizenship revoked, she said.
Belgian Interior Ministry spokesman Olivier Van Raemdonck told CNN the attacker was not Belgian and that there did not appear to be a Belgian connection to the incident.
He told RTL radio: "What our attackers want is death, symbolism, to sow panic (and) to disturb a democratic process, which is the presidential election".
Elena Worms, walking her dog near the Champs-Elysees, called the attack "destabilizing" and said she fears it will "push people to the extremes". She said her plans to vote for Fillon, a former prime minister, remain unchanged.