A man attacked a policeman with a hammer on Tuesday outside Paris’s Notre Dame Cathedral, yelling, “It’s for Syria” before he was shot and wounded by officers.

French Interior Minister Gerard Collomb said the attacker yelled as he went after officers patrolling an esplanade in front of the famous landmark. Collomb said police found kitchen knives, a hammer and other unsophisticated weapons on the wounded assailant.

The Paris prosecutor’s office said the investigation was opened Tuesday soon after the attack at in one of France’s most popular tourist areas.

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Police sealed off the area in front of the cathedral, where the attacker lay injured on the ground. Anti-terrorist prosecutors opened a probe into the incident

The incident happened around 4:30 p.m. Large numbers of police cars filled the area on the Ile de Cite island in the Seine River in the center of Paris as authorities urged people to stay away from the area.

Witnesses described a dramatic police operation in the tourist-filled area.

Lawrence Langner, a 73-year-old American visiting the neighborhood just across the Seine River from the cathedral, told The Associated Press that he suddenly heard a commotion and two detonations like gunshots.

The attack comes with France on high alert for more jihadist strikes after a weekend attack in London, where extremists used a van and knives to crush to death and kill seven people, one of them French.

Authorities in Paris asked the public to stay away from Notre-Dame, one of France’s biggest tourist attractions, situated on the banks of the Seine river in the heart of the capital.

JUST IN: Paris police shoot and injure a man who attacked an officer with a hammer at the Notre-Dame Cathedral https://t.co/QLW9Gzz3xx pic.twitter.com/EFwgJ9ac61 — CNN (@CNN) June 6, 2017

French TV reported scenes of panic during the shooting, with tourists scrambling for cover.

France is under a state of emergency and on its highest possible level of alert following a string of terror attacks that began in 2015, which have killed over 230 people.

In the last fatal attack, a policeman was shot and killed on Paris’s prestigious Champs-Elysees avenue on April 20, three days before the first round of the presidential election.

Major attacks in France targeted the Charlie Hebdo satirical magazine in January 2015 and in November that year, gunmen and suicide bombers attacked sites around Paris including the Bataclan concert hall, killing 130 people.

Then in July last year, a radicalized Tunisian man drove a lorry at high speed through a Bastille Day fireworks display on the Nice waterfront, massacring 86 people.

Since then there have been a series of smaller attacks, often targeting security forces.