The French interior ministry says the officers were shot by a man as they sat in a police van on the Champs-Elysees, the famous boulevard in the center of Paris.
In a statement from its Amaq news agency, IS gave a pseudonym for the gunman, indicating he was Belgian.
In this image made from video, police attend the scene after an incident on the Champs-Elysees in Paris, Thursday April 20, 2017.
The Islamic State group quickly claimed responsibility for the attack.
Paris police spokeswoman Johanna Primevert told AP the gunman deliberately targeted police guarding near the Franklin Roosevelt subway station.
US Vice-President Mike Pence said the Paris shooting is the "latest reminder that terrorism can strike anywhere, anytime".
Pictures of the scene in Paris showed people rushing to clear the area, and a heavy armed police presence.
United States vice president Mike Pence said the shooting was the "latest reminder that terrorism can strike anywhere, any time" and his country "will not relent in our effort to end terrorism".
French President Francois Hollande said he was convinced the circumstances of the attack in a country pointed to a terrorist act.
He fled on foot before the driver of the other auto and the passenger - a trainee police officer - caught up with him.
Within hours, ISIS claimed responsibility for the attack, which came just days ahead of a tense presidential election. But two days ago, police arrested two men in Marseille who had an arsenal in their apartment - guns, explosives. "Immediately a man got out and fired on the police vehicle, mortally wounding a police officer", Interior Ministry spokesman Pierre-Henry Brandet said.
On Friday, France said they were hunting for a new suspect based on a Belgian alert received a day earlier, but it later emerged the man had handed himself into a police station in the Belgian city of Antwerp.
Conservative candidate Francois Fillon and Marine Le Pen, leader of the far-right National Front, both talked up their tough law-and-order stances while centrist front-runner Emmanuel Macron stressed he was also up to the challenge.
The world-famous avenue was sealed off and nearby stations on the Paris Metro closed as investigations began. A foreign tourist was also slightly injured.
US President Donald Trump said the shooting resembled recent terrorist attacks. Hollande held an emergency meeting with the prime minister Thursday night and planned to convene the defense council Friday morning. "We have to be strong and we have to be vigilant".
France has been plagued by terrorism since the horrific attacks of November 2015 that left 130 people dead and hundreds injured. At the time of the shooting, all 11 presidential candidates were appearing on television. Parliament voted in December to extend the extraordinary provisions to ensure the protection of upcoming presidential and general elections.
A month ago, a would-be terrorist shot and wounded a police officer at a roadblock before being shot dead after attacking three soldiers at Orly Airport in suburban Paris.