Firefighters carry a victim on a stretcher at the scene after a shooting at the Paris offices of Charlie Hebdo, a satirical newspaper. A graphic video showing terrorists executing a wounded police officer was released on social media. Reuters

Amid the ongoing manhunt for the armed terrorists who attacked the Paris office of a French satirical magazine Charlie Hebdo Wednesday morning, graphic video of the gunmen shooting a policeman on the sidewalk has been circulating on the Web and in TV news reports. The disturbing video shows shots being fired and a police officer on the sidewalk, yelling, and then, two hooded figures run up to the downed policeman and execute him. The two figures then run into a waiting car and drive off. Parts of the video have been censored due to its disturbing nature.

The footage, apparently filmed from a rooftop or upper-floor window, was posted on social media by an unidentified person. The video has since been removed on social media, but various media sources have managed to get a hold of it before it was taken down.

The attack has so far left 12 people dead, comprising 10 journalists and 2 police officers, and five more are critically hurt. The journalist casualties included the editor and caricaturist Stéphane Charbonnier, who published under the pen name Charb. Thirty-four people were reported to have survived the attack, according to a post on Twitter. A witness said he saw multiple masked men storm into the office, according to reports. The terrorists were believed to be Islamic extremists who attacked the satirical paper for publishing cartoon depictions of the Prophet Muhammad, as any depiction of the prophet is prohibited by Islam.

French President François Hollande called the attack “an exceptional act of barbarism committed against a newspaper” and added that the attackers will be brought to justice. The NATO Secretary General echoed Hollande: “I strongly condemn the terrorist attack at the office of the Charlie Hebdo magazine in Paris today,” said Jens Stoltenberg. “This was a barbaric act and an outrageous attack on press freedom. My thoughts are with the victims and their families.”

Stoltenberg promised solidarity with France, and said all NATO allies will “stand together in the fight against terrorism.” The United States government has also condemned the attack. “The United States stands ready to work closely with the French” to help them investigate the attack, White House spokesman Josh Earnest said, speaking on MSNBC, according to Agence France-Presse. “Senior officials at the White House have been in close touch with their counterparts in France this morning.”