PARIS - A man who attacked a policeman with a hammer outside Notre Dame cathedral in Paris had pledged allegiance to the Islamic State group in a video, it emerged Wednesday, four days after an attack claimed by IS in London.

The 40-year-old man was shot and wounded by police on Tuesday after lunging at the officer in a square full of tourists in front of the cathedral.

The attack, which came with France on high alert after militants killed seven people in London on Saturday, caused panic at one of the country’s top visitor attractions. Around 1,000 people were in the cathedral at the time.

The video in which the man pledges allegiance to IS was found by police who searched the apartment he was renting in Cergy outside the French capital, the source said.

During the attack, the man had shouted “this is for Syria”, Interior Minister Gerard Collomb said.

France is part of the US-led international coalition fighting IS and has carried out air strikes against militants in Syria.

Documents found on the attacker identified him as a 40-year-old Algerian student doing a doctorate on the media at a university in eastern France. He had also been carrying kitchen knives, the interior minister said.

The man was on Wednesday placed in custody in hospital, where he is being treated for a gunshot wound to the chest.

Government spokesman Christophe Castaner said the man had “never showed any sign of radicalisation” before the attack.

The 22-year-old police officer sustained minor neck injuries in the assault.

A witness told AFP he had heard someone “shout very loudly”. “Then there was a crowd surge and people panicked. I heard two shots and saw a man lying on the ground in a pool of blood,” he said.

Heavily armed elite police had searched his apartment on Tuesday night, an AFP journalist said.

A tenant of the apartment building housing students described him as “very quiet”.

The suspect’s thesis director at the University of Lorraine, where he enrolled in 2014, said he had showed “no outward sign of an excessive adherence to Islam.”

“When I knew him, he had a pro-Western, pro-democratic outlook,” Arnaud Mercier, who said he had not heard from the suspect since November, told the French television channel BFMTV.

Notre Dame, which is situated on the banks of the Seine river in the heart of Paris, draws 13 million visitors a year.

Pictures on social media showed people sitting in the pews of the cathedral with their hands in the air - apparently at the request of authorities and police.

In September, Notre Dame was the scene of a scare after a car full of gas canisters was found parked nearby.

The car was tracked to an all-female terrorist cell, allegedly acting on the orders of Syria-based IS militants.

Tuesday’s incident came three days after extremists used a van and knives to crush to death and kill seven people enjoying a night out in London, three of them French.

France is still under a state of emergency imposed after the November 2015 attacks in Paris, when Islamic State militants killed 130 people in a night of carnage at venues across the city.

The last fatal attack in France dates to April 20, when a policeman was shot dead on Paris’s prestigious Champs-Elysees avenue, three days before the first round of the presidential election.

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

Then in July last year, a radicalised 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.