French police have named three suspects in the investigation into this Wednesday mroning shootings of 12 people at a French magazine.

The men have been named as French nationals Said Kouachi and Cherif Kouachi, in their early 30s, along with 18-year-old Hamyd Mourad. His nationality is unknown.

French police officials have said the suspects are linked to a Yemeni terror network.

Cherif Kouachi was reportedly convicted in 2008 of terrorism charges for helping channel fighters to Iraq's insurgency. He was jailed for 18 months.

Three masked gunmen stormed the offices of Charlie Hebdo, which has previously been targeted over its portrayal of the Prophet Mohammed.

They were armed with Kalashnikov rifles and a rocket-propelled grenade during the attack on Wednesday morning.

A major manhunt was launched after the men fled the scene in a black Citroen, which was later found abandoned in north-eastern Paris.

They then hijacked a white Renault Clio and drove off in the direction of the Porte de Pantin - one of the main routes out of the French capital.

The attackers called out their victims by name before opening fire during a morning editorial meeting.

They were let inside the Charlie Hebdo building by a female employee who was threatened at gunpoint along with her daughter and forced to punch in a security code to allow them inside.

The editor and a cartoonist for the newspaper, who went by the pen names Charb and Cabu, were among those killed.

Radio France chief executive Mathieu Gilet announced revealed that contributor Bernard Maris was also killed.

Two police officers were among the dead, including one assigned as Charb's bodyguard after he had received death threats and another who was shot in the head as he lay wounded on the ground outside the offices.

French President Francois Hollande has declared a national day of mourning on Thursday.

In a televised address on Wednesday he said: "We have to respond according to the crime, first of all by finding the authors of this infamy and we have to ensure that they are arrested, judged... and punished very severely.

"We must also protect all public buildings... security forces will be deployed everywhere where there could be a threat.

Our best weapon is our unity, the unity of all our citizens, nothing can divide us, nothing must separate us. Freedom will always be stronger than barbarism."

Hassen Chalghoumi, imam of Drancy mosque in the Paris suburb of Seine-Saint-Denis, said: "These are criminals, barbarians. They have sold their soul to hell. This is not freedom.

"This is not Islam and I hope the French will come out united at the end of this."

An extra 3,000 police officers have been deployed on the streets in a massive security operation, according to reports, as the security threat level in France was raised to the highest level.

Tens of thousands of people have staged silent protests in France and across the world in solidarity for the victims of the attack.

Social media users have used the hashtag #jesuischarlie to show solidarity for the victims of the shooting, with the Charlie Hebdo website also using the image as its masthead.

The shooting is one of the worst terror attacks in France in decades.

In 1995, a bomb on a commuter train blamed on Algerian extremists killed eight people at the Saint Michel metro station in Paris.

Mohamed Merah, an al Qaeda-inspired gunman, killed seven people in Toulouse in 2012, including three French soldiers and three children.