"France once again pays the price of blood, but does not give an inch to the enemies of freedom," President Emmanuel Macron said.
A man with a knife killed one person and four others were 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, but 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.
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 the attacker shouted "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.
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.
The stabbing happened at around 9 p.m. local time (3 p.m. ET), the U.S. official said.
France has been on edge after a series of terror attacks in the country.