A rally of defiance and sorrow, protected by an unparalleled level of security, will honor the 17 victims of three days of bloodshed in Paris that left France on alert for more violence.

Among the expected hundreds of thousands attendees Sunday are leaders from around the world, including the Israeli prime minister and the Palestinian president.

"We are all Charlie, we are all police, we are all Jews of France," French Prime Minister Manuel Valls said before the rally, referring to the victims that included employees at the Charlie Hebdo newspaper, shoppers at a kosher grocery and two police officers.

More than 2,000 police are being deployed to protect the demonstration, with France still on high alert while investigators determine whether the attackers were part of a larger extremist network.

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