Man attacks police with hammer outside Notre Dame Cathedral in Paris

A man armed with knives and a hammer cried "It's for Syria" and attacked a police officer outside of the world-famous Notre Dame Cathedral in Paris Tuesday afternoon. Police then shot him. The attacker's condition is unclear.

The incident prompted a huge police response and left hundreds of tourists and visitors trapped inside the church as the investigation unfolded.

The police department tweeted about the operation on Tuesday afternoon. Large numbers of police cars filled the area on the Ile de Cite island in the River Seine in the center of Paris.

"A person came up behind the police officers, armed with a hammer, and started to hit the police officer," Interior Minister Gerard Collomb told reporters. He said that one officer was lightly wounded.

Paris is under high security after a string of Islamic extremist attacks in recent years.

A witness, who works as a tech correspondent at Israel Public Cooperation, said in a tweet: "suspect tried to attack an officer shot near Notre Dame Cathedral in Paris."

"U.S. citizens should avoid the area and follow advice of French authorities," the U.S. Embassy in Paris said in an emergency message. "U.S. citizens are encouraged to monitor media and local information sources and factor updated information into personal travel plans and activities."

In early May, the U.S. State Department issued a travel alert for Europe because of a series of terror-related incidents in France, Russia, Sweden, and the U.K. "U.S. citizens should always be alert to the possibility that terrorist sympathizers or self-radicalized extremists may conduct attacks with little or no warning," the State Department said in the alert. "Extremists continue to focus on tourist locations, transportation hubs, markets/shopping malls, and local government facilities as viable targets."

Initial reports said a person allegedly assaulted an officer with a hammer, BMFTV reported. The officer fired his gun, striking the attacker.

A police union official, Cedric Michel, said a man armed with a hammer went after the police officer who was patrolling on the esplanade in front of Notre-Dame Cathedral. Michel said the attacker was "neutralized" by police.

It is unclear whether the attacker was acting alone. Paris prosecutors have opened a counterterrorism investigation into the incident.

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.

Journalist David Metreau, who said his office overlooks the square that fronts Notre Dame, tweeted that there were two blasts that sounded like shots. He posted a photo of a body lying seemingly inert on the ground.

With the Associated Press and Fox News