One policeman has been shot dead and two others wounded in central Paris, French police say, with their suspected attacker killed by security forces.
A lone gunman opened fire before being killed as he fled the scene, police say. The Champs-Elysees was sealed off.
President Francois Hollande said that he was convinced the attack was "terrorist-related".
So-called Islamic State (IS) said that one of its "fighters" had carried out the attack.
A car pulled up alongside a police bus just before 21:00 (19:00 GMT) and a man got out, opening fire with an automatic weapon at the bus.
After killing an officer, he attempted to run away while shooting at other officers, two of whom he injured.
He was then shot dead by security forces.
Paris prosecutor Francois Molins later said 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)."
Meanwhile, IS identified the attacker as Abu-Yusuf al-Baljiki, in a statement carried by its Amaq news outlet.
The whole of the Champs-Elysees was evacuated and police vehicles were lined up near a point half way up the avenue around the George V metro station, our correspondent says.
Shots were heard near the Marks & Spencer store, provoking a panicked rush away from the scene by tourists and passers-by.
Thousands of troops and police guard tourist areas of the French capital.In February, a man armed with a machete in each hand was wounded after attacking soldiers on patrol at the Louvre Museum.
The following month, a 39-year-old man was killed at Orly airport after attacking a soldier.