PARIS (CBSNewYork/AP) — The Eiffel Tower stood dark in a symbol of mourning Saturday night as France struggled to absorb the deadliest violence on its soil since World War II: coordinated gun-and-suicide bombing attacks across Paris that left at least 129 people dead and 352 injured.

President Francois Hollande vowed that France would wage “merciless” war on the Islamic State group, which claimed responsibility for the mayhem, as investigators raced to track down their accomplices and uncovered possible links to networks in Belgium and Syria.

READ MORE: Bodycam Video Shows Moments Before NYPD Lieutenant Was Shot In Ankle Apprehending Suspect In The Bronx
A picture taken on November 14, 2015 shows the Eiffel Tower with its lights turned off following the deadly attacks in Paris. (Photo credit ALAIN JOCARD/AFP/Getty Images)

A picture taken on November 14, 2015 shows the Eiffel Tower with its lights turned off following the deadly attacks in Paris. (Photo credit ALAIN JOCARD/AFP/Getty Images)

Paris prosecutor Francois Molins said three groups of attackers, including seven suicide bombers, carried out the “act of barbarism” that shattered a Parisian Friday night.

He said the attackers in the Bataclan concert hall, where 89 people died, mentioned Syria and Iraq during their rampage. Of the hundreds wounded in the six attacks, 99 were in critical condition.

Seven attackers launched gun attacks at Paris cafes, detonated suicide bombs near France’s national stadium and killed hostages inside the concert venue during a show by an American rock band — an attack on the heart of the pulsing City of Light.

A U.S. law enforcement official confirmed at least one American was killed in the attacks.

California State University, Long Beach identified the American victim as 23-year-old student Nohemi Gonzalez. The university said in a Facebook post that Gonzalez was a junior who was studying design and was in Paris on a semester abroad program.

“Nohemi was something of a star in our department. She was a shining star and she brought joy, happiness, laughter to everybody she worked with,” said Michael LaForte‎, a lecturer at the CSULB Department of Design.

LaForte posted a remembrance of Gonzalez on Facebook Saturday morning.

Nohemi Gonzalez (Credit: Strate – Ecole de Design/Facebook)

Nohemi Gonzalez (Credit: Strate – Ecole de Design/Facebook)

“Yesterday, we, the CSULB Design Family, lost Nohemi Gonzalez in the Paris terrorist attacks. Nohemi was a kind, thoughtful, generous and talented student, dear to all who knew her,” he said.

On Saturday, Parisians lined up to donate blood and pay respects at memorials, CBS2’s Tony Aiello reported.

Paris tourist Virginia Davis is a New Yorker who witnessed the 9/11 attacks.

“So we have lived through this, we know how painful it is for the French, we know how painful it is,” she said. “As the president said yesterday, it is for all people who believe in human rights and dignity and we stand with the French and it is a very sad day for all humanity.”

Hollande, who declared three days of national mourning and raised the nation’s security to its highest level, called the carnage “an act of war that was prepared, organized, planned from abroad with internal help.”

Web Extra: Attacks Timeline | Photos | Videos | CBSN | Continuing Coverage

The Islamic State group’s claim of responsibility appeared in Arabic and French in an online statement circulated by IS supporters. It was not immediately possible to confirm the authenticity of the admission, which bore the group’s logo and resembled previous verified statements from the group.

The statement mocked France’s involvement in air attacks on suspected IS bases in Syria and Iraq, noting that France’s air power was “of no use to them in the streets and rotten alleys of Paris.”

Grief, alarm and resolve spread across Europe on Saturday as officials raced to piece together information on the seven attackers.

Molins, the prosecutor, said all seven attackers wore identical suicide vests containing the explosive TATP. Molins said one was identified from fingerprints as a French-born man with a criminal record.

In addition, a Syrian passport found near the body of another attacker was linked to a man who entered the European Union through a Greek island last month.

Authorities in Belgium conducted raids in a Brussels neighborhood Saturday and made three arrests linked to the Paris attacks. Justice Minister Koen Geens told the VRT network that the arrests came after a car with Belgian license plates was seen close to the Bataclan theater.

Prosecutor’s office spokeswoman Agnes Thibault-Lecuivre said authorities couldn’t rule out the possibility that other militants involved in the attack remained at large.

The violence raised questions about security for the millions of tourists who come to Paris and for world events routinely hosted in the normally luminous capital, where 1,500 troops were deployed to support police in restoring order and reassuring a frightened populace.

The NYPD increased security at all high-profile locations Friday evening in response to the attacks. Heavily armed security personnel were seen throughout the city, including a strong presence in Times Square.

French Interior Minister Bernard Cazeneuve announced that all public demonstrations would be banned until Thursday and local governments would have the option to impose nightly curfews. He said police and military reinforcements would be deployed to key public buildings.

Many of Paris’ top tourist attractions closed Saturday, including the Eiffel Tower, the Louvre Museum and the Disneyland theme park east of the capital.

Parisians expressed shock, disgust and defiance in equal measure. Hundreds of soccer fans departing the stadium Friday night waved French flags and sang impromptu choruses of the national anthem, “Le Marseillaise.”

As a shrine of flowers expanded along the sidewalk, a lone guitarist sang John Lennon’s peace ballad, “Imagine.”

READ MORE: Several People Shot Outside Queens Laundromat, Police Investigating

Photos: France, World Mourn Paris Attacks

Hollande said the attacks meant France would increase its military efforts to crush IS. He said France – which besides bombing suspected IS targets in Syria and Iraq as part of the U.S.-led coalition also has troops fighting militants in Africa — “will be merciless toward the barbarians of Islamic State group.”

Early Saturday morning, Hollande met with top government and security officials.

On Friday night, President Barack Obama called the attacks on Paris an attack on all of humanity.

“This is a heartbreaking situation. And obviously those of us here in the United States know what it’s like. We’ve gone through these kinds of episodes ourselves,” the president said. “And whenever these kinds of attacks happened, we’ve always been able to count on the French people to stand with us. They have been an extraordinary counterterrorism partner, and we intend to be there with them in that same fashion.”

Reflecting fears in other European capitals of the risk of coordinated or copycat attacks, the British government mounted a meeting of its own emergency COBRA intelligence committee. Italy said it, too, was raising security levels on borders and major public places.

British Prime Minister David Cameron said British citizens were among the casualties in Paris, but he declined to provide specifics. He warned that the threat posed by Islamic State “is evolving.”

Friday night’s militants launched at least six gun and bomb attacks in rapid succession on apparently indiscriminate civilian targets.

Three suicide bombs targeted spots around the national Stade de France stadium, north of the capital, where Hollande was watching an exhibition soccer match. Fans inside the stadium recoiled at the sound of explosions, but the match continued.

Around the same time, fusillades of bullets shattered the clinking of wine glasses in a trendy Paris neighborhood as gunmen targeted a string of cafes, which were crowded on an unusually balmy November night. At least 37 people were killed, according to Paris Prosecutor Francois Molins.

The attackers next stormed the Bataclan concert hall, which was hosting the American rock band Eagles of Death Metal. They opened fire on the panicked audience and took members hostage. As police closed in, three detonated explosive belts, killing themselves, CBS2’s Alice Gainer reported.

“The people who are dead in the stairs, broken windows, it’s like a war scene,” said one witness.

Another attacker detonated a suicide bomb on Boulevard Voltaire, near the music hall, the prosecutor’s office said.

Video shot from an apartment balcony and posted on the Le Monde website Saturday captured some of that horror as dozens of people fled from gunfire outside the Bataclan down a passageway to a side street.

At least one person lies writhing on the ground as scores more stream past, some bloodied or limping. The camera pans down the street to reveal more fleeing people dragging two bodies along the ground. A woman and two others can be seen clinging to upper-floor balcony railings in an apparent desperate bid to stay out of the line of fire.

Le Monde said its reporter who filmed the scene from his apartment balcony, Daniel Psenney, was shot in the arm after he stopped filming, when he went downstairs to help someone who had collapsed in the alley.

A tall, sturdy 38-year-old concert-goer named Sylvain collapsed in tears as he recounted the attack, the chaos and his escape during a lull in gunfire.

“I was watching the concert in the pit, in the midst of the mass of the audience. First I heard explosions, and I thought it was firecrackers.

“Very soon I smelled powder, and I understood what was happening. There were shots everywhere, in waves. I lay down on the floor. I saw at least two shooters, but I heard others talk. They cried, ‘It’s Hollande’s fault.’ I heard one of the shooters shout, ‘Allahu Akbar,”’ Sylvain told The Associated Press. He spoke on condition that his full name not be used out of concern for his safety.

He was among dozens of survivors offered counseling and blankets in a municipal building set up as a crisis center.

Jihadis on Twitter immediately praised the attackers and criticized France’s military operations against Islamic State extremists.

France has been on edge since January, when Islamic extremists attacked the satirical newspaper Charlie Hebdo, which had run cartoons of the Prophet Muhammad, and a kosher grocery. Twenty people died in those attacks, including three shooters.

French authorities are particularly concerned about the threat from hundreds of French Islamic radicals who have traveled to Syria and returned home with skills to mount attacks.

“The big question on everyone’s mind is: Were these attackers — if they turn out to be connected to one of the groups in Syria — were they homegrown terrorists or were they returning fighters?” said Brian Michael Jenkins, a terrorism expert and senior adviser to the president of the Washington-based RAND Corporation.

The Paris carnage was the worst in a series of attacks claimed by the Islamic State in the past three days. On Thursday, twin suicide bombings in Beirut killed at least 43 people and wounded more than 200, and 26 people died Friday in Baghdad in a suicide blast and a roadside bombing that targeted Shiites.

The militant group also said it bombed a Russian plane that crashed in Egypt’s Sinai Peninsula on Oct. 31, killing 224 people.

A U.S. official said intelligence officials were not aware of any threats before the series of attacks.

MORE NEWS: COVID In New York: Mask Mandates Not Being Re-Imposed Just Yet As Concern Grows Over Delta Variant

(TM and © Copyright 2015 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2015 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)