PARIS, Jan. 8 -- One minute's silence was observed all over the country on Thursday; bells of Notre Dame rang at midday and flags fly at half-mast for three days in memory of the victims of Charlie Hebdo shooting in Paris.

In a prime-time TV evening address, French President Francois Hollande had declared Thursday a mourning day, calling all French citizens to unite together at this difficult time in France.

"Our best weapon is our unity. Nothing can divide us, nothing can stop us, and nothing can separate us...Liberty will always be stronger than barbarity," he said.

On Wednesday, two masked and heavily armed men stormed offices of the satirical magazine Charlie Hebdo and killed 12 people.

In November 2011, the magazine's headquarters was firebombed after it put an image of the Prophet Mohammad on its cover.

In its last published cartoons, the weekly mocked Abu Bakr al-Baghdadi, the leader of the Islamic State, which seized majot towns in Iraq and Syria.

Identified as Cherif Kouachi, 32, and his 34-year-old brother Said, the two suspects from Paris region are still at large after 24 hours of the shooting. Reports said they were located in the Aisne in north eastern France.

A nationwide manhunt is widened to find the "armed and dangerous men".

According to some reports, Cherif Kouachi had previously been trialed on terrorism charges and served 18 months in prison.