PARIS (REUTERS/AFP) - World leaders including Muslim and Jewish statesmen linked arms to lead an estimated million-plus French citizens through Paris in an unprecedented march under high security to pay tribute to victims of Islamist militant attacks.
People also poured into the streets in other European cities, and even Israel to demonstrate their solidarity with the marchers in France.
In Paris, police said the turnout was "without precedent" but too large to count. One organiser said he had indications it could be between 1.3 and 1.5 million people. Some commentators said the last street presence in the capital on this scale was at the Liberation of Paris from Nazi Germany in 1944.
President Francois Hollande and leaders from Germany, Italy, Israel, Turkey, Britain and the Palestinian territories among others, moved off from the central Place de la Republique ahead of a sea of French and other flags. Giant letters attached to a statue in the square spelt out the word Pourquoi?" (Why?) and small groups sang the "La Marseillaise" national anthem.
Some 2,200 police and soldiers patrolled Paris streets to protect marchers from would-be attackers, with police snipers on rooftops and plain-clothes detectives mingling with the crowd. City sewers were searched ahead of the vigil and underground train stations around the march route are due to be closed down.
The march mostly went ahead in a respectful silence, reflecting shock over the worst militant Islamist assault on a European city in nine years. For France, it raised questions of free speech, religion and security, and beyond French frontiers it exposed the vulnerability of states to urban attacks.
Two of the gunmen had declared allegiance to Al-Qaeda in Yemen and a third to the militant Islamic State in Iraq and Syria (ISIS). All three were killed during the police operations in what local commentators have called "France's 9/11", a reference to the September 2001 attacks on U.S. targets by Al-Qaeda.
"Paris is today the capital of the world. Our entire country will rise up and show its best side," said Hollande.
"Fantastic France! I am told there could be as many as 1.3 million to 1.5 million of us in Paris," Francois Lamy, the lawmaker charged by the ruling Socialist Party with organising the rally, tweeted.
Isabelle Dahmani, a French Christian married to a Muslim, Mohamed, brought their three young children to show them there is nothing to fear.
Their nine-year-old daughter burst into tears watching the news this week, Isabelle said, adding she had asked if "the bad men are coming to our house?" The grieving families of those who died in the shootings led the march, alongside the representatives of around 50 countries.
Patrick Pelloux, a Charlie Hebdo columnist, fell sobbing into the arms of Hollande in an emotional embrace.
With dozens of world leaders present, security in the jittery French capital was beefed up, with police snipers stationed on rooftops and plain-clothes officers among the crowd in a city still reeling from the Islamist attacks.
"Today, Paris is the capital of the world," Hollande said. "The entire country will rise up." More than a million also rallied in cities outside the capital and marches were held in several cities across Europe, including Berlin, Brussels and Madrid.
Italian Prime Minister Matteo Renzi pledged that Europe "will win the challenge against terrorism". Earlier he had tweeted using the hashtag #jesuischarlie (I am Charlie), which has already been used more than five million times.
US President Barack Obama was represented by Attorney General Eric Holder, who took part in an emergency meeting of interior ministers to discuss the threats from Islamic extremism.
The ministers urged a strengthening of the EU external borders to limit the movement of extremists returning to Europe from the Middle East and said there was an "urgent need" to share air passenger information.
Hollande has warned his grieving country not to drop its guard in the face of possible new attacks. Ahead of the march, he met representatives from the Jewish community who said authorities had agreed to deploy soldiers to protect Jewish schools and synagogues in France "if necessary".
At least 700,000 more joined vigils in other cities across France.
In London, several landmarks including Tower Bridge were lit up in the red white and blue colours of the French national flag in a show of support for the event in Paris. Fifty-seven people were killed in an Islamist militant attack on London's transport system in 2005.
Seventeen people, including journalists and police, were killed in three days of violence that began with a shooting attack on the weekly Charlie Hebdo known for its satirical attacks on Islam and other religions as well as politicians. It ended on Friday with a hostage-taking at a Jewish deli in which four hostages and the gunman were killed.
Hours before the march, a video emerged featuring a man resembling the gunman killed in the kosher deli. He pledged allegiance to the ISIS extremist group and urged French Muslims to follow his example.
"We're not going to let a little gang of hoodlums run our lives," said Fanny Appelbaum, 75, who said she lost two sisters and a brother in the Nazi concentration camp at Auschwitz. "Today, we are all one."
Zakaria Moumni, a 34-year-old Franco-Moroccan draped in the French flag, agreed: "I am here to show the terrorists they have not won - it is bringing people together of all religions."
German Chancellor Angela Merkel, British Prime Minister David Cameron and Italian Prime Minister Matteo Renzi were among 44 foreign leaders marching with Hollande. United Nations Secretary-General Ban Ki-moon, Israel's Benjamin Netanyahu - who earlier encouraged French Jews to emigrate to Israel - and Palestinian President Mahmoud Abbas were also present.
Immediately to Hollande's left, walked Merkel and to his right Malian President Ibrahim Boubacar Keita. France intervened to help fight Islamist rebels there two years ago to the day.
In a rare public display of emotion by two major-power leaders, cameras showed Hollande embracing Merkel, her eyes shut and forehead resting on his cheek, on the steps of the Elysee before they headed off to march.
After world leaders left the march, Hollande stayed to greet survivors of the Charlie Hebdo attack and their families.
While there has been widespread solidarity with the victims, there have been dissenting voices. French social media have carried comments from those uneasy with the "Je suis Charlie"slogan interpreted as freedom of expression at all cost. Others suggest there was hypocrisy in world leaders whose countries have repressive media laws attending the march.
The head of France's 550,000-strong Jewish community, Roger Cukierman, the largest in Europe, said Hollande had promised that Jewish schools and synagogues would have extra protection, by the army if necessary, after the killings.
Far-right National Front leader Marine Le Pen, whom analysts see receiving a boost in the polls due to the attacks, said her anti-immigrant party had been excluded from the Paris demonstration and would instead take part in regional marches.
In Germany, a rally against racism and xenophobia on Saturday drew tens of thousands of people in the eastern German city of Dresden, which has become the centre of anti-immigration protests organised by a new grassroots movement called PEGIDA.
A building of the newspaper Hamburger Morgenpost, which like many other publications has reprinted Charlie Hebdo cartoons, was the target of an arson attack and two suspects were arrested, police said on Sunday.
German newspaper Bild said the bloodshed in France could signal the start of a wave of attacks in Europe, citing communications by ISIS leaders intercepted by US intelligence.
In Israel, hundreds rallied in Jerusalem and Ramallah on Sunday in separate shows of solidarity with France over the attacks in Paris.
More than 500 people gathered in Jerusalem in front of a screen reading in French "Jerusalem is Charlie", a correspondent said.
Participants observed a minute's silence, holding signs reading in French "I am Charlie" and "I am a French Jew", and in Hebrew "Israel is Charlie".
"This is an attack on all of us - on the Jewish people, on freedom of media and expression," Jerusalem Mayor Nir Barkat said.
"We are all French Jews, Jerusalem is Charlie," he added in French.
Jerusalem chief rabbi Shlomo Amar said a prayer for the 17 victims, including four Jews killed in a Paris supermarket on Friday who will be buried in Israel.
But for some participants, the massive show of support in France following this week's attack on the offices of satirical weekly Charlie Hebdo was tinged with bitterness.
Pierre Besnainou, a longtime leader in the French-Jewish community who recently immigrated to Israel, said such an outpouring would have been welcome after previous attacks targeting French Jews.
"The mobilisation after Charlie leaves a bitter taste, since we felt very alone after Toulouse," he said, referring to attacks in which an Islamic extremist shot dead three children and a teacher at a Jewish school in 2012.
"Despite the efforts of the French security agencies, we won't be able to protect our Jews in France," he said.
Israeli Prime Minister Netanyahu, who flew to Paris on Sunday to attend a massive solidarity march, has called for Jews living in France to leave for Israel following the attacks.
Dozens of Palestinians also held a rally in the West Bank city of Ramallah, as Palestinian president Mahmud Abbas participated too in the Paris march.
Waving Palestinian and French flags, they held up banners reading "Palestine stands with France against terrorism."
Gaza paid tribute to the victims during a candlelit vigil in the enclave.
Hamas, the de facto rulers of Gaza, condemned the assault on Charlie Hebdo in a statement on Saturday which failed to refer to the subsequent attack on the Jewish supermarket.