A French boy residing in Nicaragua holds up a card that reads, "I am Charlie", to pay tribute to the victims of the shootings in France at the offices of the satirical weekly newspaper Charlie Hebdo and a Jewish deli, in Managua January 10, 2015. [Photo/Agencies]

Ollivier Souchard, a French-born New York resident who brought his family and friends, explained the fierce support for freedom of expression behind Charlie Hebdo's provocative images.

"What we are afraid of is less freedom for more security, it's muzzling," Souchard said.

Making a fist and tapping it over his heart, he added, "Satirical cartoons are essential to us, they're essential to France. We were raised with great cartoons, but you Americans don't like to hurt people with cartoons - but you should hurt people!"

"Charlie Hebdo would not exist in America," Souchard said.

Souchard said he has been in touch with his friend Philippe Lancon, a Charlie Hebdo columnist who is recovering from surgery after being shot in the face in the attack.

Earlier on Saturday, Prime Minister Manuel Valls urged a massive turnout on Sunday's "silent march" which Europe's main leaders will attend.

"This will be an unprecedented event that will undoubtedly go down in history and which will show the strength and dignity of the French people," Valls said.

"Terrorism wants us to hide away. The best answer to that is what French people are doing since Wednesday with spontaneous rallies," he added.