French authorities say a man was shot and injured by the police after he attacked an officer with a hammer outside Paris's Notre Dame Cathedral on June 6.
Authorities said the situation was under control, and the attacker was taken to a hospital. The officer sustained only minor injuries.
Armed police sealed off the area in front of the cathedral after the incident.
French Interior Minister Gerard Collomb said the attacker was carrying the identity card of an Algerian student and that he was armed with a hammer and knives.
Collomb told journalists that authorities at this point believe the attacker acted alone and shouted "This is for Syria!" during the incident.
The counterterrorism office of the Paris prosecutor's office announced it had opened a probe into the incident. The attacker's motives were unknown. The incident comes just three days after Islamist militants killed seven people in London in a knife and van attack.
Police urged people to stay away from the area, writing on Twitter that an operation is under way on the square in front of the cathedral. French TV reported panicked tourists fleeing for cover.
France is under a state of emergency imposed after a series of terrorist attacks in 2015 and 2016, mostly claimed by the Islamic State extremist group, that left over 230 people dead.
Several of the attacks have targeted police or security officials. In April, an attacker shot at a police van in the center of the capital, killing one officer and wounding two. The attacker was shot dead by police.
In February, a man with a machete at the Louvre Museum threatened security guards, who shot and disabled him.
In addition, there have been several major attacks in France over the last two years. In January 2015, terrorists killed 12 people at the editorial office of the Charlie Hebdo satirical magazine.
In November 2015, 130 people were killed by gun-and-bomb attacks on several Paris locations, including the Bataclan concert hall.
In July 2016, a man drove a truck through a crowd celebrating Bastille Day in the southern city of Nice, killing 86 people.
On June 11, France is due to go to the polls in the first round of parliamentary elections, with recently elected President Emmanuel Macron hoping to gain a majority in the National Assembly.