PARIS (AP) -- Masses of people joined with world leaders to fill Paris streets Sunday in a rally for unity that officials said was the largest demonstration in French history. Hundreds of thousands more marched in cities around the country and the world to repudiate a three-day terror spree around the French capital that killed 17 people and left the three gunmen dead.

Their arms linked, more than 40 world leaders headed the somber procession - Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas; Ukrainian President Petro Poroshenko and Russian Foreign Minister Sergey Lavrov - setting aside their differences for a demonstration that French President Francois Hollande said turned the city into "the capital of the world."

Millions of people streamed through the streets behind them and across France to mourn the victims of deadly attacks on a satirical newspaper, a kosher supermarket and police officers - violence that tore deep into the nation's sense of wellbeing in a way some compared to Sept. 11 in the United States.

"Our entire country will rise up toward something better," Hollande said.

Details of the attacks continued to emerge, with new video showing one of the gunmen pledging allegiance to the Islamic State group and detailing how the attacks were going to unfold. That gunman, Amedy Coulibaly, was also linked to a new shooting, two days after he and the brothers behind a massacre at satirical newspaper Charlie Hebdo were killed in nearly simultaneous police raids.

The attacks tested France's proud commitment to its liberties - liberties that authorities may now curtail to ensure greater security. Marchers recognized this as a watershed moment.

"It's a different world today," said Michel Thiebault, 70.

Illustrating his point, crowds cheered police vans as they wove through the crowds Sunday - a rare sight at the many demonstrations that Parisians have staged throughout their rebellious history, when protesters and police are often at odds.

Many shed the aloof attitude Parisians are famous for, helping strangers with directions, cheering and crying together. Sad and angry but fiercely defending their freedom of expression, the marchers mourned the dead and brandished pens and flags from around the world.

Giant rallies were held throughout France and major cities around the world, including London, Madrid and New York - all attacked by al-Qaida-linked extremists - as well as Cairo, Sydney, Stockholm, Tokyo and elsewhere.

In Paris, the Interior Ministry said, "the size of this unprecedented demonstration makes it impossible to provide a specific count," noting that the crowds were too big to fit on the official march route and spread out into other streets.

Later, the ministry said 3.7 million marched throughout France, including roughly between 1.2 and 1.6 million in Paris, but said a precise account is impossible given the enormity of the turnout.

French news media estimated up to 3 million people took part in the Paris march - more than the numbers who took to Paris streets when the Allies liberated the city from the Nazis in World War II.

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