A police officer has been shot dead and two other wounded after a gunman opened fire on Paris’ Champs-Elysees on April 20.
The 39-year-old gunman has been identified from papers left in his car, but French officials are yet to release his name.
Local media say the suspect lived in Paris’ suburbs, and had been seen as a potential Islamist radical.
The attacker was killed by security forces on the Champs-Elysees.
President François Hollande is to chair a security cabinet meeting, as France readies for April 23 presidential poll.
Francois Hollande said he was convinced the attack was “terrorist-related”, adding that the security forces had the full support of the nation and a national tribute would be paid to the fallen policeman.
Meanwhile, ISIS said one of its “fighters” had carried out the attack.
A car pulled up alongside a police bus just before 21:00 and a man got out, opening fire on the bus with an automatic weapon, Interior Ministry spokesman Pierre-Henry Brandet said.
After killing an officer, the man attempted to run away while shooting at other officers, two of whom he injured, the spokesman added.
The attacker was then shot dead by security forces.
The whole of the Champs-Elysees was evacuated.
Overnight, a property in the eastern Parisian suburb of Chelles was searched by investigators, who want to know who else – if anyone – may have known about the gunman’s plans.
Paris prosecutor François Molins said shortly after the shootings that “the attacker’s identity is known and has been verified”.
“I won’t reveal it, because investigations and raids are already under way, in particular to establish whether there is any evidence or not of complicity (in this attack),” Francois Molins said, adding that more information would be released on April 21.
According to French media, the gunman served several years in prison for firing on police officers with a gun in the early 2000s.
More recently the intelligence services identified him as a potential Islamist radical.
Meanwhile, ISIS identified the attacker as Abu-Yusuf al-Baljiki, in a statement carried by its Amaq news outlet.
The 11 candidates standing in April 23 closely fought presidential election were engaged in a final joint TV appearance to argue their policies as the attack happened.
Marine Le Pen, of the far-right Front National, tweeted: “I feel for and stand by our security forces, who have been targeted again.”
Center-right contender François Fillon also went on Twitter to pay “tribute to the security forces who give their lives to protect ours”.
Independent centrist Emmanuel Macron said during his TV appearance that it was a president’s “first duty to protect” and he expressed his “solidarity” with the police.
Marine Le Pen, Francois Fillon and Emmanuel Macron have announced they are canceling campaign events scheduled for April 21, the last day of canvassing for votes.
Jean-Luc Mélenchon, standing for the far left, tweeted: “I strongly feel for the policemen killed and wounded and their families. Terrorist attacks will never go unpunished, accomplices never forgotten.”