French interior ministry spokesman Pierre Henry Brandet told the BBC in Paris that seven people had been detained for questioning, all of whom were related, or connected in some way, to the two main suspects - Cherif and Said Kouachi. Of the two brothers Mr Brandet said Cherif was "well known" to French authorities, and his brother Said was "less well known". Hamyd Mourad, the man who handed himself in, has an alibi - he was at school at time, according to BBC chief international correspondent Lyse Doucet.

There has been shooting this morning south of Paris, with one police officer injured. Police say there is no link to the Charlie Hebdo attack.

Prime Minister David Cameron has offered the assistance of British intelligence to help French agencies investigate the atrocity, it was announced earlier.

British cartoonist Bill Tidy says his colleagues should "pull back" from criticising religions. Mr Tidy, whose 'Cloggies' cartoons were published in Private Eye, told BBC Radio Derby cartoonists should be rethinking who they satirise.

Image source, Getty Images

A picture of a newspaper stand in New Delhi, India, gives some indication of the scale of the news coverage of the attack around the world.

BBC's Paris correspondent Lucy Williamson said ministers and security chiefs had started to arrive at the Elysee Palace for the crisis meeting, which will be chaired by President Francois Hollande.

One of the men being hunted, 32-year-old Cherif Kouachi, 32, has a terrorism conviction for his involvement in a network sending fighters to Iraq. He and elder brother Said should be considered "armed and dangerous", police say.

French journalist Agnes Poirier speaking from Paris told BBC Breakfast: "A lot of people in France feel quite powerless." She said a lot of people were asking, "Is this war?".

A total of seven arrests were made overnight, all family and friends of the suspects, a spokesman for the French interior ministry has told the BBC.

Terrorist expert David Lowe told BBC Breakfast: "It shows how difficult it is for police and security services to try and prevent this type of this attack. Small cells operating on their own are difficult to pick up." He described the killings as "cold and calculated", and that the attackers were clearly "proficient in firearms", and showed a sense of calm as they they left the scene.

In that interview with RTL radio this morning, French Prime Minister Manuel Valls said preventing another attack "is our main concern" as he explained why authorities released photos of the two men along with a plea for witnesses to come forward, AP news agency reports.

French President Francois Hollande is expected to hold crisis meetings at the Elysee Palace about the attack on Thursday. Meanwhile, UK Home Secretary Theresa May will chair an emergency Cobra meeting to formulate Britain's response to the attack.

More from Prime Minister Valls - he also said the two suspects were known to police and were "no doubt" being followed before the attack.

"Several arrests" were made overnight as police hunt two brothers suspected of carrying out the Charlie Hebdo attacks, the French Prime Minister Manuel Valls has told French radio.

Image source, Getty Images

Staff members of Agence France-Presse news agency display placards in solidarity with the victims of the shooting at the Paris office of the satirical newspaper Charlie Hebdo.

Image source, Getty Images

News of the attack has made headlines around the world. Here (pictured) a newspaper vendor in Pakistan arranges the morning papers.

Although the hunt for the two brothers Cherif and Said Kouachi continues, a third man Hamyd Mourad, 18, surrendered to police, after hearing his name on the news in connection with the attack, a judicial official announced earlier.

The slogan "Je Suis Charlie" ("I am Charlie") has been used in solidarity with the victims of the attacks by people around the world. Here, a woman carried a sign near the French ambassador's residence in Tokyo.

Image source, Reuters

Journalist Luc Herman works in the same building as Charlie Hebdo. He arrived at work on Wednesday just after the shots were heard. He told BBC Breakfast: "We heard heavy fire from just across the door. It's is a major attack on the freedom of the press. Our people are really under shock."

Here's what we know about yesterday's attacks.