One man sought in the deadly shooting at a French satirical paper has turned himself in, and police hunted Thursday for two heavily armed men with possible links to al Qaeda in the military-style, methodical killing of 12 people at the office of a satirical newspaper.

President Francois Hollande, visiting the scene of France's deadliest such attack in more than half a century, called the assault on the weekly newspaper Charlie Hebdo “an act of exceptional barbarism.“

France raised its terror alert system to the maximum, Attack Alert, and bolstered security with more than 800 extra soldiers to guard media offices, places of worship, transport and other sensitive areas.