There are reports this morning that the youngest of the three Paris shooting suspects, Hamyd Mourad, has surrendered to police.
The 18-year-old suspect handed himself into police late last night after seeing his name circulated on social media, according to sources who spoke to AFP, it has been reported.
This follows a security operation which took place in the French city of Reims last night.
Earlier, police identified the three gunmen who stormed the offices of a satirical newspaper in Paris killing 12 people, according to reports.
French police had named the suspects as brothers Said and Cherif Kouachi (aged in their 30s) as well as Hamyd Mourad (18)
Celebrated French cartoonists Cabu, Charb, Tignous and Wolinski were all killed in the attack on the Paris offices of the weekly paper Charlie Hebdo. Two police officers guarding the paper were also killed.
The gunmen escaped in a waiting car, according to video filmed by witnesses.
WARNING: FOOTAGE BELOW IS EXTREMELY GRAPHIC
Four of those injured were said to be "between life and death" today.
Tonight, crowds are gathering in central Paris in protest and solidarity against the killings. A rally is being held by France's national journalist union.
Many protesters have adopted the slogan #JeSuisCharlie, holding up banners and placards with the words.
Shocking terrorist attack in Paris should remind us all that violent fundamentalism is very much a European problem and threat— Simon Coveney (@simoncoveney) January 7, 2015
France raised its security alert to the highest level and reinforced protective measures at houses of worship, stores, media offices and transportation.
French media to be put under police protection according to Le Figaro, quoting source in police. #Charliehebdo— Adèle Smith (@adelesmithNYC) January 7, 2015
The French president Francois Hollande called the shootings a terrorist attack "without a doubt".
The murders in Paris are sickening. We stand with the French people in the fight against terror and defending the freedom of the press.— David Cameron (@David_Cameron) January 7, 2015
Top government officials held an emergency meeting and Mr Hollande planned a nationally televised address this evening. Schools across the French capital closed their doors.
The dead include two men who went by pen names: Charb - the editor and a cartoonist as well - and the cartoonist Cabu, spokeswoman Agnes Thibault-Lecuivre of the Paris prosecutor's office confirmed.
Cabu - whose real name was Jean Cabut - was the cartoonist behind a February 2006 front page of Charlie Hebdo depicting Muhammad, following the controversy after Danish newspaper Jyllands-Posten published sketches of the Muslim prophet.
Today's events show why Adams 'joking' about shooting editors is not funny. Some maniacs do.— Mairia Cahill (@mairiac31) January 7, 2015
The Islamic State group has repeatedly threatened to attack France. Just minutes before the attack, Charlie Hebdo had tweeted a satirical cartoon of that extremist group's leader giving New Year's wishes.
Another cartoon, released in this week's issue and entitled "Still No Attacks in France," had a caricature of an extremist fighter saying "Just wait - we have until the end of January to present our New Year's wishes."
Charlie Hebdo cartoonist Corinne "Coco" Rey has told a French newspaper of the moment she encountered the two attackers as they entered the office.
"I had gone to get my daughter at nursery.
"When I arrived in front of the door of the building of the paper, two men hooded and armed brutally threatened us.
"They wanted to come in, go up. I pressed in the code.
"They shot on Wolinski, Cabu... it lasted 5 minutes... I had hidden under my desk... they spoke French perfectly... they said they we're al-Qaeda."
Cédric Le Béchec, a 33-year-old estate agent, witnessed the attack on the satirical magazine.
He said that the men arrived in a black car, stopping in the middle of the street. One of them was carrying a rocket-propelled grenade. They were dressed in black military-style clothing.
Mr Le Bechec said that before launching the assault, the attackers approached another man in the street saying, “Tell the media that this is Al Qaeda in Yemen.”
The police arrived five minutes later after the assault on the magazine's offices.
Mr Le Béchec said that the two attackers fled at the wheel of a grey Renault Clio. The vehicle’s owner was being questioned by the police.
French President Francois Hollande went to the scene of the shooting at Charlie Hebdo, a satirical weekly that has drawn repeated threats for its caricatures of the Prophet Mohammed, among other controversial sketches.
A Charlie Hebdo journalist has told French newspaper Le Monday the staff didn’t have ‘any great concern despite the threats’.
“These past few months we didn't have any great concern despite the threats. Naturally, our offices were under police protection, which reminded us of the threats,” he said.
“Charb [the publishing director] was under police protection but he moved around without his policemen, which was a sign he wasn't worried all the time.”
Charb had been under special high-profile figure protection since the publication of a Mohammed cartoon in 2011 that caused controversy.
Witness Benoit Bringer told the TV station:"About a half an hour ago two black-hooded men entered the building with Kalashnikovs (rifles). A few minutes later we heard lots of shots," he said, adding that the men were then seen fleeing the building."
A witness said multiple gunmen were involved. It is reported the gunmen used machine guns in the attack.
According to French newspaper Le Monde, the attackers 'spoke French without any accent'.
It is believed the incident took place just after 10.30am during an editorial meeting.
Several videos of the attack have been uploaded online. In one piece of footage, filmed by a man taking refuge on a nearby rooftop, the men can be heard shouting "Allahu Akbar" (God is great) during the attack.
Union official Luc Poignard said the attackers escaped in two vehicles following the incident at the weekly Charlie Hebdo.
Benoit Bringer, a journalist with Agence Premiere Ligne - who saw the attack, told the iTele network he saw several masked men armed with machine guns.
He said two officers arrived on bicycles, then - apparently unarmed - they left.
Charlie Hebdo’s lawyer Richard Malka said the magazine’s offices had been “under police protection since the Mohammed cartoon affair right up until today”.
“Charb was under special high-profile figure protection. The threats were constant. It is frightening,” he added.
It is being reported by Le Figaro that several French media offices are now being put under police protection.
France is already on high alert after calls last year from Islamist militants to attack its citizens and interests in reprisal for French military strikes on Islamist strongholds in the Middle East and Africa.
Late last year, a man shouting "Allahu Akbar" ("God is greatest") injured 13 by ramming a vehicle into a crowd in the eastern city of Dijon. Prime Minister Manuel Valls said at the time France had "never before faced such a high threat linked to terrorism".
A firebomb attack gutted the headquarters of Charlie Hebdo, a publication that has always courted controversy with satirical attacks on political and religious leaders, in November 2011 after it put an image of the Prophet Mohammad on its cover.
The last tweet on Charlie Hebdo's account mocked Abu Bakr al-Baghdadi, the leader of the Islamic State, which has taken control of large swathes of Iraq and Syria.
FBI Director James Comey said the U.S. agency is working with French law enforcement to bring those responsible to justice.
Meanwhile Jyllands-Posten, the Danish newspaper that originally published the inflammatory Prophet Mohammed cartoons in 2005, has reportedly stepped up its security.
"Surveillance and the level of security in and around our headquarters in Copenhagen and in (the west Danish city of) Viby has been increased," an internal Jyllands-Posten email said, according to Danish paper Berlingske.
"We are following closely the situation in connection with the attack on Charlie Hebdo in Paris earlier today.
British Prime Minister David Cameron described the attack as sickening as the White House condemned the attack in 'strongest possible terms'.
Speaking to the House of Commons today, he said; "I'm sure the whole House will want to join me in condemning the barbaric attack on an office of a magazine in Paris, in which it is report ten or more people may have been killed.
"While details are still unclear, I'm know that this House and this country stands united with the French people in opposition to all forms of terrorism, and we stand squarely for free speech and democracy. These people will never take us off those values."
Meanwhile, German Chancellor Angela Merkel said "This abominable act is not only an attack on the lives of French citizens and their security,"
She added: "It is also an attack on freedom of speech and the press, core elements of our free democratic culture. In no way can this be justified."
The United Nations Security Council condemned the "barbaric and cowardly terrorist attack" and called for the perpetrators to be brought to justice.
"The members of the Security Council strongly condemned this intolerable terrorist act targeting journalists and a newspaper," the 15-member council said in a statement.
A terrorist attack on the offices of the French satirical magazine 'Charlie Hebdo' has left 12 people dead in the country's worst terrorist incident for 50 years. Gunmen shouted "Allahu akbar" (God is Great) as they picked off their targets. This is how the attack unfolded.
Charlie Hebdo Attacks
Just over 30 years ago, in October 1984, the Provisional IRA bombed the Grand Hotel in Brighton. British prime minister Margaret Thatcher, a bete noire of republicans since the hunger strikes, and her entire cabinet were staying in the hotel for the Conservative Party conference. This terrorist act killed five people, but narrowly missed its principal target, Mrs Thatcher. In the aftermath of the explosion, the IRA issued a chilling statement: "Today we were unlucky, but remember we only have to be lucky once."
Charlie Hebdo Attacks
We'd forgotten about 'Charlie Hebdo'. In 2011, the satirical magazine, firmly rooted in the anti-clericalism of the French left, was firebombed after it published an edition poking fun at Islam: "100 lashes if you don't die of laughter", read the cover.
Charlie Hebdo Attacks
Journalists have led thousands tweeting the hashtag "Je Suis Charlie" in messages of solidarity with victims of the attack at the Paris office of French satirical weekly Charlie Hebdo.