Police check passers-by near the Champs Elysees in Paris after a shooting which left one officer dead and two wounded.
The attacker had been flagged as an extremist, according to two police officials, speaking on condition of anonymity because they weren't authorized to publicly discuss the investigation.
They also reported he was convicted of attempted homicide in 2003 in shootings on two police officers.
The Islamic State of Iraq and Syria (ISIS) has claimed responsibility for the shooting on Paris' Champs-Elysees in which a gunman killed a police officer and left two others gravely wounded.
Speaking during a televised debate around the time of Thursday's attack, Fillon said there was "no room for pursuing today or tomorrow an electoral campaign because first of all we have to demonstrate our solidarity with the police officers".
The incident comes just three days before French voters cast ballots in the first round of the Presidential election.
Jihadist-inspired assaults have killed more than 230 people in France since 2015, with numerous victims being people who had gone out for the evening.
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Many children were trapped inside the vehicle and most of the fatalities were declared dead at the site of the accident. The bus driver also died while the driver of the truck survived.
Molins said he would reveal the shooter's identity in a press conference Friday, adding that officers were searching the man's residence in Chelles in the Paris suburb of Seine-et-Marne.
US President Donald Trump on Thursday condemned the Paris terrorist attack, saying there is a need to stay strong and vigilant. Two of the main candidates, conservative Francois Fillon and centrist Emmanuel Macron, canceled campaign events Friday. The Islamic State claimed responsibility in a message posted on a jihadi channel, and the Paris prosecutor said he had opened a terrorism investigation.
British Prime Minister Theresa May also spoke to Hollande. The attacker, a 29-year-old Egyptian, was seriously injured.
A French prosecutor said the attacker emerged from a auto and used an automatic weapon to shoot at the officers outside a department store at the centre of the boulevard.
Mr Fillon said the fight against "Islamist totalitarianism" should be the next president's priority, calling for better co-operation between world powers.
French media have named him as Karim Cheurfi, although this has not been officially confirmed.
"We had to hide our customers in the basement", Choukri Chouanine, manager of a restaurant near the site of the shooting, said, saying there was "lots of gunfire". She said he appeared to act alone.
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To understand why, we should first ask the question of what China's strategic interests are with regards to the Korean peninsula. It test-fired a missile on Sunday that exploded within seconds of launch, following a grand military parade on Saturday.
"She won't be able to protect our citizens", Macron said.
A man emerged from the vehicle and opened fire on the van with an "automatic weapon", killing one officer instantly, Brandet said.
The Champs-Elysées has been closed and authorities are telling people to avoid the area.
Officers searched the home of the dead attacker in a town east of Paris, a police source said.
The French interior ministry said it was too early to tell what the motive was for the attack in the Champs-Elysees but President Francois Hollande said he was convinced it was a terrorist attack..
The country has witnessed a series of Islamic militant attacks perpetrated mostly by young men, killing more than 230 people in the span of two years.
3 Feb 2017 - A machete-wielding Egyptian man shouting "Allahu akbar" attacks French soldiers at Paris's Louvre Museum - he is shot and wounded.
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Fortunately, I had far more good than bad times at Upton Park. "We are talking about an England captain, a true leader". Bilic added: "We are going to see".