A police officer has been killed and two others are seriously injured after a shooting in one of the most popular areas of Paris.
The gunman is believed to have deliberately targeted the officers and was known to security services.
He was then shot dead and an anti-terror investigation is under way into the attack in the heart of the French capital.
ISIS has claimed it was behind the shooting and named the attacker as Abu Yusuf al Beljiki, suggesting he was a Belgian.
Police have issued an arrest warrant for a second suspect who had arrived in the country by train from Belgium.
The gunman had opened fire outside a Marks and Spencer store on the Champs-Elysees - one of Paris' main shopping streets and an area popular with tourists.
Security has been tight in the country, coming just days before the first round of France's presidential election on Sunday.
President Francois Hollande has said he is convinced the attack was terror-related.
Tweeting following the attack, he said his thoughts are with the dead policeman's family and relatives of the wounded officers - adding that a national day of mourning will now be held.
The gunman armed with a Kalashnikov parked his Audi behind a police van, then got out and opened fire on the vehicle, according to a witness called Chelloug who heard six shots.
He said: "I thought they were firecrackers. In fact, he (the gunman) was hidden behind the van and shooting at the police. I think he hit a policeman. As soon as the policeman opened the door of the van, he fell."
Another witness identified only as Ines told French television station BFM that she heard a shooting, saw a man's body on the ground and the area was quickly evacuated by police.
Despite the attacker being killed, police are still on high alert and officers have been seen pointing their weapons at members of public as they clear the area.
There had been reports one of the injured officers had died in hospital of his wounds but that was later denied by officials.
The gunman attacked as the officers were guarding an area near the Franklin Roosevelt metro station, not far from the Arc de Triomphe on Thursday night.
Many police vehicles are at the scene and a helicopter hovered overhead.
Authorities are now searching the home of the gunman in the east of Paris.
Although an anti-terror probe has been opened, other reports said the shooting could have been an attempt at an armed robbery.
US President Donald Trump said the shooting resembled recent terrorist attacks.
He said: "First of all, our condolences from our country to the people of France. Again, it is happening, it seems.
"It looks like another terrorist attack. What can you say? It just never ends. We have to be strong and we have to be vigilant, and I have been saying it for a long time."