A police officer was killed and two others were seriously injured when a gunman opened fire late Thursday on the famed Champs-Élysées in Paris before he was shot dead, officials said. The Islamic State group quickly claimed responsibility for the attack.

French prosecutors have opened a terrorism investigation into the attack on the officers, which took place at 8:50 p.m. local time.

Paris Prosecutor Francois Molins said authorities have identified the 39-year-old gunman but did not name him publically. Officials are still assessing whether he had accomplices, he said.

Molins said the gunman used an assault rifle, and at least one location in the eastern Paris suburbs is being searched as officials work to learn more information about the attacker.

"The identity of the attacker is known and has been checked," he said. "I will not give it because investigations with raids are ongoing."

In a statement from its Amaq news agency, ISIS named the attacker Abu Yousef Al-Baljiki, "The Belgian," adding that he was "one of the Islamic State fighters."

The claim of responsibility came unusually swiftly for the group, which has been losing territory in Iraq and Syria. It also referred to the attacker as one of the "fighters," rather than the "soldiers" of the Islamic State.

Paris police spokeswoman Johanna Primevert told The Associated Press the attacker, who is believed to have acted alone, targeted police guarding the area near the Franklin Roosevelt subway station at the center of the avenue popular with tourists.

French President Francois Hollande said he is convinced the circumstances of the Paris shooting points to a terrorist act.

"We need to realize our security, law enforcement forces targeted have the full support of the nation," he said in an address to the nation.

Hollande said security forces would be vigilant during the forthcoming presidential election.

"We shall be of the utmost vigilance, especially in relation to the election," he said, adding that an emergency meeting of security, defense and intelligence top officials would be held on Friday.

The French Interior Ministry said the shooting attack "deliberately targeted" police officers guarding the area. Ministry spokesman Pierre-Henry Brandet said the gunman came out of a car and opened fire on the police vehicle with an automatic firearm akin to a "war weapon."

"We are faced with a specifically high terrorist threat," he told reporters.

No tourists or pedestrians were injured in the shooting, according to Brandet.

Coming back from a run, Champs Elysées is a mess.. #paris pic.twitter.com/CTwRuqDCAQ — Ralph (@vanderpauw) April 20, 2017

The attacker was known by secret service in France as an extremist, officials confirmed to Fox News.

Paris police and soldiers sealed off the area around the Champs-Elysees after the attack, ordering tourists back into their hotels and blocking people from approaching the scene. Emergency vehicles blocked the wide avenue that cuts across central Paris between the Arc de Triomphe and the Tuileries Gardens, an area normally packed with cars and tourists.

Subway stations in the area were also closed off on Thursday night while police secure the scene.

A 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.

Attentat probable sur les Champs Elysée pic.twitter.com/KSRkR5DiM1 — yas (@yasmystic) April 20, 2017

A Paris resident told the Associated Press the gunfire sent scores of tourists fleeing into side streets.

Badi Ftaiti, a Tunisian-born mason who has spent three decades in Paris, told the AP tourists "were running, running....Some were crying. There were tens, maybe even hundreds of them."

President Trump said the shooting "looks like another terrorist attack" during a news conference with Italian Prime Minister Paolo Gentiloni, and sent his condolences to France.

TRUMP ON PARIS SHOOTING: 'IT JUST NEVER ENDS'

The State Department said it was "closely following the disturbing situation," adding that it was "ready to assist in any way the French authorities would find helpful."

"Our Embassy in Paris is monitoring the situation closely. We urge U.S. citizens in Paris to contact family members and loved ones to notify them that you are safe, to avoid the area, and monitor local news for updates," the statement read.

The incident on Thursday was similar to two recent attacks on soldiers providing security at prominent locations around Paris, one at the Louvre museum in February and one at Orly airport last month.

The attack came three days before the first round of balloting in France's tense presidential election.

Security is high preceding the vote after police said they arrested two men Tuesday in what they described as a thwarted terror attack.

French conservative presidential candidate Francois Fillon on Thursday evening said he was canceling a planned election campaign outing on Friday after the shooting.

France has been in a state of emergency following a series of terrorist attacks, including the the November 2015 attacks, which targeted the Bataclan concert hall and Stade de France sports arena in Paris and the deadly truck attack in Nice on Bastille Day in July 2016.

The state of emergency has been extended by several parliamentary votes and remains in effect.

Fox News' Catherine Herridge and The Associated Press contributed to this report.

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