An axe-wielding man wearing a fake explosives vest was shot dead by officers outside a Paris police station on Thursday and prosecutors said he was carrying an Islamic State flag.
The incident sent shockwaves through the city, one year after a pair of Islamists launched a deadly raid on the editorial offices of satirical magazine Charlie Hebdo.
The unidentified man was armed with an axe, the kind used for slaughtering animals, prosecutors said. He seemed to be trying to enter the police station in northern Paris.
Prosecutors, who have opened an investigation, said the man was carrying an Islamic State flag and a handwritten note in Arabic.
Islamic State claimed partial responsibility for the Charlie Hebdo attacks and full responsibility for a series of attacks in November.
The incident - coming exactly one year after the Charlie Hebdo attacks - immediately prompted fears of terrorism in a city that has endured two sensational attacks in the last year.
"It is much too early to talk about a terrorist act," Interior Ministry spokesman Pierre-Henry Brandet told France Info. "One has to be careful. This is about an attack."
The AFP news agency, citing justice officials, said the fake explosives device consisted of a bag with tape, out of which a cable protruded.
Although there were no explosives, the item looked real enough to prompt authorities to have his body checked by an explosives robot before they approached and gave the all clear.
Montmartre, a district popular with tourists, was cleared during the incident. No motive was reported.
Terrorists attacked Charlie Hebdo's offices on January 7, 2015, the first incident of three days of terror in the French capital that ultimately saw 17 civilian deaths, along with the deaths of three attackers killed as police closed in on them.
On November 13, a team of terrorists launched coordinated strikes against bars, a theatre and a football stadium, causing 130 deaths.