After returning from a trip to the state of Arizona, the president went straight to the French mission on Thursday, where he signed a book of condolences over the deadly attack, stood in silence for about a minute and then shook hands with Ambassador Gerard Araud.

"On behalf of all Americans, I extend our deepest sympathy and solidarity to the people of France following the terrible terrorist attack in Paris," Obama wrote.

"As allies across the centuries, we stand united with our French brothers to ensure that justice is done and our way of life is defended."

On his return to the capital city, Obama convened a call with his national security team on his Air Force One plane, in which he was updated on the French investigation into Wednesday's shootings in the offices of Charlie Hebdo, a satirical weekly, White House spokesman Josh Earnest told reporters.

"When we see terrible incidents like this that strike in other countries, we want to make sure that we're doing every single thing that we can at US facilities, military and diplomatic, around the globe to protect Americans there," Earnest said.

French police continue a manhunt for two brothers suspected of opening fire with assault rifles in the offices of Charlie Hebdo and exchanging shots with police then in the street before fleeing by car on Wednesday.

Another suspect, the youngest at 19, turned himself in to police that night and was put in custody. Obama spoke to French President Francois Hollande on Wednesday, offering American for help with the identification, apprehension and prosecution of the killers.

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