Hackers have targeted about 19,000 French websites since a rampage by Islamic extremists left 20 dead last week, France's cyberdefence official said Thursday, as the president tried to calm the nation's inflamed religious tensions.

France is on edge since last week's attacks, which began Jan. 7 at the offices of the satirical newspaper Charlie Hebdo. The paper, repeatedly threatened for its caricatures of the Muslim Prophet Muhammad, was burying several of its slain staff members Thursday.

Calling it an unprecedented surge, Adm. Arnaud Coustilliere, head of cyberdefence for the French military, said about 19,000 French websites had faced cyberattacks in recent days, some carried out by well-known Islamic hacker groups.

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French President Francois Hollande, right, and Jack Lang, president of the Institut du Monde Arabe (Arab institute), walk past the Arab Institute building bearing the message 'We are Charlie', in Paris Thursday. (Ian Langsdon/Reuters)

The attacks, mostly relatively minor denial-of-service attacks, hit sites as varied as military regiments to pizza shops but none appeared to have caused serious damage, he said.

"What's new, what's important, is that this is 19,000 sites — that's never been seen before," Coustilliere said. "This is the first time that a country has been faced with such a large wave of cyber-contestation."

Coustilliere called the attacks a response to the massive demonstrations against terrorism that drew 3.7 million people into the streets Sunday across France. He pointed to "more or less structured groups" that used tactics like posting symbols of jihadist groups on companies' websites.

Two of the Paris terror attackers claimed allegiances to al-Qaeda in Yemen, and another — who targeted a kosher supermarket — to the Islamic State group.

Military authorities have launched round-the-clock surveillance to protect the government sites still coming under attack.

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French President Francois Hollande speaks Thursday during a visit to the Institut du Monde Arabe (Arab institute) in Paris. (Ian Langsdon/Reuters)

According to Arbor Networks, a private company that monitors threats to the Internet, in the past 24 hours alone, France has been the target of 1,070 denial of service attacks. That's about a quarter as many as the United States, but the U.S. hosts 30 times as many websites.

The terror attacks in Paris occurred in an atmosphere of rising anti-Semitism in France, and have prompted scattered violence against Muslims and Muslim sites around France in an apparent backlash. They have also put many French Muslims on the defensive.

Since the attacks, French justice officials have been cracking down by arresting dozens of people who glorified terrorism or made racist or anti-Semitic remarks.

French President Francois Hollande insisted Thursday that any anti-Muslim or anti-Semitic acts must be "severely punished." He said France's millions of Muslims should be protected and respected, "just as they themselves should respect the nation" and its strictly secular values.

Kerry to France

"In the face of terrorism, we are all united," he said at the Institute of the Arab World in Paris, noting that Muslims are the main victims of Islamic extremist violence.

U.S. Secretary of State John Kerry, who is heading to France later Thursday, said he wants to "share a big hug with Paris and express the affection of the American people for France and for our friends there who have been through a terrible time."

With 120,000 security forces deployed to prevent future attacks, nerves jumped overnight when a car rammed into a policewoman guarding the president's palace. Prosecutors and police said, however, the incident at the Elysee Palace had no apparent links to last week's shootings.

The car carrying four people took a one-way street in the wrong direction then drove off when the police officer tried to stop them. The officer sustained slight leg injuries, police said. Two people were later arrested and two others in the car fled.

Dismay, anger

Customers lined up again Thursday to try to get copies of Charlie Hebdo's first edition since the attacks, which again had Muhammad on its cover. Even though it has a special increased print run of 5 million copies, it sold out before dawn Thursday in Paris kiosks for a second straight day.

Some Muslims, who believe their faith forbids depictions of the prophet, reacted with dismay or anger to the new cover. Pakistani lawmakers passed a resolution and marched outside parliament Thursday to protest the publication.

A leader of Yemen's al-Qaeda branch officially claimed responsibility for the attacks at Charlie Hebdo, saying in a video online that the slayings were in "vengeance for the prophet."

But U.S. and French intelligence officials are leaning toward an assessment that the Paris terror attacks were inspired by al-Qaeda but not directly supervised by the group. That view would put the violence in the category of homegrown terror attacks, which are extremely difficult to detect and thwart.