More than 1 million people and 40 world leaders participated in a march to honor the victims of deadly terrorist attacks in Paris -- a manifestation that French President Francois Hollande said turned the city into "the capital of the world."
The unity march in downtown Paris was being led by French and foreign leaders accompanied by relatives of the 17 victims of the attacks by radical Islamists against the satirical weekly Charlie Hebdo, a French police woman, and a Jewish supermarket.
One of the organizers estimated that between 1.3 million and 1.5 million people attended the march between Place de la Republique and Place de la Nation.
The Associated Press news agency quoted the French Interior Ministry as saying the rally was the largest in French history.
French President Francois Hollande linked arms with German Chancellor Angela Merkel and other leaders, among them British Prime Minister David Cameron, Italy’s Prime Minister Matteo Renzi, Israeli Prime Minister Benjamin Netanyahu, and Palestinian leader Mahmud Abbas.
Ukrainian President Petro Poroshenko and Russian Foreign Minister Sergei Lavrov, whose countries are engaged in a violent struggle in Ukraine, also took part.
The United States is represented by U .S. Attorney General Eric Holder.
At the start of the march, the participants observed a minute of silence. Various groups of people also sang the French anthem, La Marseillaise.
Later in the day, President Hollande, accompanied by Israel's Netanyahu attended a ceremony at the Grand Synagogue in Paris.
Some 5,500 police and troops have been deployed in Paris to ensure the security of the march.
The security forces include police snipers on rooftops and plainclothes detectives who will mingle in the crowd to protect marchers from would-be attackers.
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Paris Unity March To Honor Terror Victims Begins
WATCH: Paris Unity March To Honor Terror Victims Begins
The ancient sewer tunnels of Paris also were searched ahead of the vigil and underground train stations around the march route were to be closed.
National Front Not Attending
More than 600,000 people reportedly joined rallies in various French towns on January 11, including Lyon, Bordeaux, and Marseille.
France's far-right National Front (FN) held a demonstration of its own against terrorism, after being excluded from the unity rally in Paris.
Party leader Marine Le Pen led a rally in the FN-controlled southern town of Beaucaire after denouncing what she called the "exclusion" of her party from Paris march.
Across Europe, tens of thousands of people also attended rallies.
Some 20,000 people marched through the Belgian capital Brussels, holding banners saying "United against hate" and "Freedom of speech."
In Berlin, some 18,000 joined the march while in Madrid's Plaza de Sol, hundreds descended on the streets with red, white, and blue French flags, and singing La Marseillaise.
Many of the demonstrators joined a separate rally held by hundreds of Muslims at Madrid's Atocha station, the scene of the worst terror attack in Spanish history in 2004, to condemn violence committed in the name of Islam.
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World Leaders March In Paris To Honor Terror Victims
WATCH: World Leaders March In Paris To Honor Terror Victims
Elsewhere in Europe, about 3,000 people turned out in Stockholm, many holding pens in the air, and more than 1,000 people gathered in London's Trafalgar Square, also raising pencils to the sky. Several London landmarks were lit in the colors of the French national flag.
About 25,000 people marched in the Canadian city of Montreal in solidarity with France. Hundreds of people staged support rallies in Jerusalem, Beirut, and in the West Bank city of Ramallah.
Three days of terrorist violence in and around the French capital ended with a raid on January 9 that resulted in the deaths to the northeast of Paris of Al-Qaeda-linked brothers Cherif and Said Kouachi, the suspects in the January 7 massacre of 12 people at the office of Charlie Hebdo.
An almost simultaneous raid by security forces on January 9 at a Jewish market in eastern Paris also killed Amedy Coulibaly, who is said to have shot dead a French policewoman on January 8 and four hostages at the market on January 9.
French security forces are still searching for Hayat Boumeddiene, a woman initially described as an accomplice who was with Coulibaly when he killed the policewoman in southern Paris.
French authorities have described her as “armed and dangerous."
Turkish and French security sources said on January 10 that Boumeddiene is now thought to have entered Turkey on January 2, several days before the violence began, and may have crossed into Syria.
Meanwhile, posthumous video emerged January 11 of Coulibaly, in which he is pledging allegiance to the Islamic State group.
In the video, apparently filmed over several days, Coulibaly can be seen with a gun, exercising and giving speeches in front of an IS emblem. He defends the attacks carried out on Charlie Hebdo, police and the Jewish store.
At one point, he says Charlie Hebdo will be attacked "tomorrow" and that he and the brothers who carried out the attack were coordinating.
Security has been tight ahead of the rally.
U.S. Attorney General Eric Holder said January 11 there was no "credible information" as yet that Al-Qaeda was behind the attacks in France that have killed 17 people.
Holder, speaking from Paris, said, "At this point, we don't have any credible information that would allow us to make a determination as to which organization was responsible."
But Holder voiced concern about so-called lone wolf attacks in the United States by Islamist militants inspired by Al-Qaeda affiliates.