The killing of policeman Xavier Jugele by 39-year-old gunman Karim Cheurfi on the Champs Elysees was the latest in a string of terror attacks in France that began in 2015.
An attacker emerged from a vehicle in Paris Thursday and used an automatic weapon to shoot at officers in the center of the Champs-Elysees.
Far-right candidate Marine Le Pen said the attack showed the time for naivety "is over".
Said by polls to be running neck-and-neck with Le Pen, he tore into her claims that previous attacks wouldn't have happened under her watch. Cheurfi also had addresses of police stations written on bits of paper in his auto, he said.
Her chief rival in the race for the French presidency, centrist Emmanuel Macron, pointedly waved an European Union flag from the podium at a campaign rally the next day.
The attack overshadowed the final day of campaigning for the first round of the French election, which takes place on Sunday.
No one - including Le Pen - is expected to win the 50% of the vote necessary to win the presidency outright on Sunday.
As Paris got back to business, municipal workers in white hygiene suits were out before dawn to wash down the sidewalk where the assault took place - a scene now depressingly familiar after multiple attacks that have killed more than 230 people in France over two years. "It just never ends". Bernard Cazeneuve, the Socialist prime minister, accused Le Pen of electoral opportunism in the face of a tragedy.
Speaking a short time afterward, Fillon said that if elected he would focus on the destruction of ISIS. "This fight for freedom and for the security of the French people must be the priority of the next five-year term".
Macron appealed to voters not to succumb to fear. "Don't yield to fear, don't yield to division and intimidation". "The choice that you have to make on Sunday must be a choice for the future".
There are four leading candidates in a race that is still too close to call.
The Islamic State group claimed responsibility for Thursday's shooting via its Amaq news agency, naming the attacker as Abu Yousif al-Belgiki. The warrant said the man had arrived in France by train from Belgium.
French President François Hollande convened a meeting of the country's defense council Friday.
The dead officer was 30, Paris Prosecutor Francois Molins said. A German tourist was also injured. A Belgian prosecutor said there was no indication the attacker was Belgian, reported France 24. He shot two officers in 2001 after being stopped by a police, according to the source.
While in detention, Cheurfi had also shot and wounded a prison officer after seizing his gun. He was jailed again in 2013 for lesser offenses and released on probation two years later. He was briefly placed under house arrest and investigators discovered knives and masks in his home but no evidence linking him to terror groups, Molins said.
In a statement from her campaign headquarter in Paris, she asked the government and judicial authorities to handle the case of all individuals on the French territory known for "their adhesion to the enemy's ideology".
Belgian security officials had warned French counterparts before the attack that El Osri was a "very unsafe individual en route to France" aboard the Thalys high-speed train. Three of his family members have been placed in detention, the French interior ministry announced on Friday.
Earlier this week French authorities arrested two men in Marseille who were allegedly planning an attack in a run-up to the election.
Trump himself weighed in at a news conference in Washington following the attack.
"Because our country is at war, the response must be global, total", she said, according to Bloomberg.
A Downing Street spokesman said: "The UK strongly condemns the appalling terrorist attack in Paris".