A man with a knife killed one person and left four others injured in central Paris Saturday night before the suspect was killed by police, authorities said, and a prosecutor said the attack is being investigated by a counter-terrorism unit.

Two of those wounded were seriously injured, police said on Twitter. Police said the attacker was dead. A senior U.S. intelligence officer briefed on the situation said police fatally shot the suspect, who appeared to indiscriminately stab people near the city's Opera.

France's interior minister, Gerard Collomb, said early Sunday local time that all four people injured are out of danger. He said the victim was a 29-year-old man.

Judicial sources confirmed to NBC News on Sunday morning that the suspect was born in 1997 in the Russian region of Chechnya, where Islamic extremism has long simmered. His two parents were taken into custody and are being questioned.

A motive in the stabbing is unclear, but French President Emmanuel Macron said on Twitter that "France once again pays the price of blood, but does not give an inch to the enemies of freedom," and "I salute on behalf of all the French people the courage of the policemen who neutralized the terrorist."

Paris Prosecutor Francois Molins said on French radio that the investigation into the knife attack is in the hands of the counter-terrorism unit, and that several witnesses heard the attacker shout "Allahu akbar," Arabic for "God is great." But Molins did not discuss a motive.

The U.S. official briefed on the situation said witnesses stated that the suspect looked emotionally disturbed and was pacing and muttering before the incident. Paris and U.S. officials said the stabbing is being investigated as a terror attack.

A judicial source close to the investigation told NBC News on Sunday that the suspect was known to French authorities and was on the country's watchlist for signs of Islamic radicalization.

The Islamic State terror group claimed in a statement from its Amaq media arm claiming that the attacker was a "soldier" of the group, according to security consulting firm and NBC News partner Flashpoint Intelligence.

The statement contains no evidence to back up the group's claim, and it was not clear whether the suspect was inspired by or even a follower of the terror group.

Chechen leader Ramzan Kadyrov, meanwhile, said Sunday that while the attacker was born in the Russian republic, he hadn’t received a new passport in 20 years.

“He was only born in Chechnya, and his growing up, the formation of his personality, his views and persuasions occurred in French society," Kadyrov said in a statement, according to the Associated Press.

"I consider it necessary to state that all responsibility for the fact that Khasan Azimov went on the road of crime lies completely with the authorities of France,” Kadyrov added.

Forensic officers and French police stand in Monsigny street in Paris after one person was killed and several injured by a man armed with a knife, who was shot dead by police in Paris on May 12, 2018. Geoffroy Van Der Hasselt / AFP - Getty Images

The stabbing happened at around 9 p.m. local time (3 p.m. ET), the U.S. official said.

French Prime Minister Edouard Philippe said in an interview broadcast by BFMTV that the attacker was killed nine minutes after police were called to the scene.

BFM television interviewed an unnamed witness in a restaurant who said a young woman was at the entrance when "a man arrived and attacked her with a knife." A friend came to her aid and the attacker left, "hitting on all the doors, all the shops," the witness told BFM. He turned onto another street, and everyone scattered, the witness said.

"I was having a drink with friends and we heard a boom," a witness named Gloria, who had been in a nearby bar, recounted on Saturday night. She said she went outside to see what happened and "I saw a guy lying on the ground."

France has been on edge after a series of terror attacks in the country.