Heavily armed soldiers are patrolling the streets of Paris today as three gunmen who attacked the offices of controversial magazine Charlie Hebdo remain on the loose.

The French government has upped security at train stations, places of worship, newspaper offices and public spaces this afternoon after 12 people, including police officers and journalists, were shot dead earlier today.

Soldiers wearing green berets, dressed in combat fatigues, and carrying Famas assault rifles have been pictured in front of the Eiffel Tower and inside Montparnasse railway station.

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Lockdown: The streets of Paris are being patrolled by soldiers dressed in combat fatigues and carrying Famas assault rifles this afternoon after a terror attack killed 12 people earlier in the day

Armed: Three gunmen who attacked the offices of controversial magazine Charlie Hebdo this morning remain on the run this afternoon, causing authorities to heighten security

Secure: Troops have been deployed to places of worship, public spaces and train stations (pictured, Montparnasse station in Paris) following on from the attack earlier today

French authorities have now raised the threat alert to the highest level possible, while the British Foreign Office has issued a warning to those travelling to the city.

Three gunmen are believed to have forced their way into the offices of magazine Charlie Hebdo this morning and asked for senior staff by name in fluent French before executing them.

The attack is believed to be in retaliation for cartoon images published by the magazine which depicted the Prophet Mohammed, which is deeply offensive to Muslims.

Hebdo had its offices burned down in 2011 after publishing an issue of the magazine entitled Sharia Weekly which claimed to be guest edited by the holy figure, and featured the cover slogan '100 lashes if you don't die laughing'.

On guard: The French government has raised the threat alert to the highest level possible while the British Foreign Office has issued a warning to those travelling to the city

Vanished: Nothing has been seen of the three gunmen who attacked the Hebdo offices since this morning when they were seen fleeing towards the east of the city in a stolen car

Tense: French soldiers patrol at Montparnasse railway station in Paris this afternoon after 12 people, including police officers, were killed in an terror attack

The editor and head cartoonist Stephane Charbonnier, who is believed to be among the dead, was also put on Al Qaeda's most wanted list last year after spending months under police protection.

Officers were also detailed to guard the offices, according to Charbonnier's lawyer, and today French police were confirmed to be among the dead.

Video footage from the scene of the killing shows two of the attackers climbing out of a black Citroen before cutting an officer down with five precise shots.

They advance to where the man is laying using military-style techniques, covering each other as they run, before executing him with a single round to the head.

Also among the dead are some of France's most revered cartoonists including Georges Wolinski, Bernard 'Tignous' Verlhac, Jean Cabut and Bernard Maris.

President Francois Hollande described the bloodbath as a 'barbaric attack against France and against journalists' and vowed to hunt down those responsible.

Hunted: Police are hunting these two gunmen and a third accomplice after the highly-trained killers raided the offices of a controversial magazine this morning over cartoons it published of the Prophet Mohammed

Controversial: Stepahne Charbonnier, also known as Charb, the editor of Charlie Hebdo, wsa among those killed after the gunmen got into their building then called the senior staff by name before killing them

The attack took place during the publication's weekly editorial meeting, meaning all the journalists would have been present.

Corrine Ray, a young mother and cartoonist who survived the massacre, today told how she was forced to allow the killers into the office.

She described hiding under a desk during the shooting, saying the editors were called out by name before being executed.