At least 100 people have died in a popular Paris concert hall where attackers seized hostages , an official said, one of at least six terror attacks that unfolded across the city in the deadliest violence Paris has seen since World War II.

French President Francois Hollande declared a state of emergency and announced that he was closing the country’s borders. The violence spread fear through the city and exceeded the horrors of the Charlie Hebdo carnage just 10 months ago.

Paris police officials said security officials had launched an assault on the concert hall, killing at least two attackers. One described “carnage” inside the building, saying the attackers tossed explosives at the hostages.

In addition to the deaths at the concert hall, a police official said 11 people were killed in a Paris restaurant in the 10th Arrondissement and other officials said at least three people died when bombs went off outside a stadium.

All of the officials spoke on condition of anonymity because they were not authorized to be publicly named in the quickly moving investigation.

There was no immediate claim of responsibility for the attacks, and no clear picture of how many attackers were involved and if any were on the run. Jihadists on Twitter immediately praised the attack and criticised France’s military operations against Islamic State extremists.

Hollande, who had to be evacuated from the stadium when the bombs went off outside, said in a televised address that the nation would stand firm and united.

“This is a terrible ordeal that again assails us,” he said. “We know where it comes from, who these criminals are, who these terrorists are.”

US President Barack Obama, speaking to reporters in Washington, called the attacks on Paris “outrageous attempt to terrorise innocent civilians” and vowed to do whatever it takes to help bring the perpetrators to justice.

Earlier yesterday, two explosions were heard outside the Stade de France stadium north of Paris during a France—Germany friendly football match. A police union official said there were two suicide attacks and a bombing that killed at least three people.

The official, Gregory Goupil of the Alliance Police Nationale, whose region includes the area of the stadium, said explosions went off simultaneously near two entrances and a McDonalds.

The attack comes as France has heightened security measures ahead of a major global climate conference that starts in two weeks, out of fear of violent protests and potential terrorist attacks. Hollande canceled a planned trip to this weekend’s G—20 summit in Turkey, which was to focus in large part on growing fears of terrorism carried out by Islamic extremists.

European Union chief Jean—Claude Juncker said he was “deeply shocked” by the attacks.

France has been on high alert since the jihadist attacks in January against Charlie Hebdo magazine and a Jewish supermarket that left 17 dead.

Several other attacks have been foiled through the year.

More than 500 French fighters are thought to be with IS in Syria and Iraq, according to official figures, while 250 have returned and some 750 expressed a desire to go there.

The government announced last week that it was restoring border checks as a security measure for UN climate talks that start in Paris at the end of this month.

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