The French authorities say they know the identity of the man who shot dead a policeman and wounded two others on the Champs Elysees in Paris.
The gunman was killed when officers returned fire.
The attacker emerged from a car and used an automatic weapon to shoot at officers outside a Marks & Spencer store at the centre of the Champs-Elysees.
Prosecutors say they won't release his name until they know whether or not he was working alone.
French officials said the suspect was previously flagged as an extremist.
Eyewitness Badi Ftaiti told the Press Association:
"They were running, running... Some were crying. There were tens, maybe even hundreds of them."
Police have launched a terrorism investigation and the so-called Islamic State extremist group claimed responsibility for the attack.
The world-famous avenue was sealed off and nearby stations on the Paris Metro closed as investigations began.
French police warned the public to stay away from the area and armed officers were at the scene.
Tourists were warned to go back to their hotels and to let family and friends know they were safe.
The UK Foreign Office said:
"If you're in the area and it is safe to do so, contact your friends and family to tell them you are safe."