Gunmen have attacked the offices of French magazine Charlie Hebdo in Paris, killing 12 people including the editor and celebrated cartoonists
The hunt is on for three suspects, named by police as Hamyd Mourad and brothers Said Kouachi and Cherif Kouachi.
It is the deadliest terror attack in France since 1961 during the Algerian war
President Hollande said it was an act of "extreme barbarity", with many foreign leaders also condemning the attack
In 2011, the satirical publication was firebombed after naming the Prophet Muhammad as its "editor-in-chief"
Charles-Henry Boudet
France 3 TV journalist
is in Reims where a police anti-terror raid is taking place and has tweeted, external this picture from the scene:
Image source, @MisterCHCHMeryl Cumins: Commiserations to the injured and the families of the dead. Fraternity, Equality and most of all, Liberty. Where freedom of speech is an alien concept there can be only tyranny.
AFP has more details from that police raid reportedly taking place in Reims in north-eastern France. A member of France's elite anti-terror unit has called on journalists at the scene to remain "vigilant", warning that there would "a showdown" or that the suspects could escape, the agency says.
Damian Grammaticas
BBC News
tweets, external: Multiple reports of police raids in Reims as police search for #CharlieHebdo suspects, 1 of 3 identified is from Reims
Police say an anti-terror raid is under way in the north-eastern city of Reims, according to the AFP news agency.
BBC correspondent Fergal Keane reports that tensions over the role of Islam have "sharpened" in France over recent years.
He adds: "Along with that there is resentment over French policy in the Arab world which has radicalised many youth."
The BBC's Hugh Schofield has written about how the attack on Charlie Hebdo will be felt in France.
He says today "will remain engraved in the national memory."
In response to Wednesday's attack, at least three Danish newspapers are planning to print copies of cartoons from Charlie Hebdo, according to the BBC's Malcolm Brabant in Copenhagen.
But none of the Copenhagen press are planning to reprint the 12 Danish cartoons of the Prophet Muhammad that ignited anger in some areas of the Muslim world seven years ago. Yet security has been tightened at all of the country's media outlets as a result of the massacre.
The editor of the tabloid BT said he would be running with Charlie Hebdo's most controversial cover - one that showed a weeping Muhammad overwhelmed by fundamentalists, lamenting that it was hard being loved by idiots.
BBC News website reader: My heart bleeds and I'm shaken to the core by what happened to fellow journalists that only did their job (and did it well).
Former CIA counter-terrorism analyst Aki Peritz tells BBC World News that that the attacks appear to have been "very professional, well thought out, well researched and well executed".
He says it is significant that apart from the police, the only other targets were journalists and nobody else inside the Charlie Hebdo office was killed.
The Paris Normandie newspaper has expressed its solidarity with those killed in today's attack, publishing a front page which alters the name of the publication in honour of Charlie Hebdo.
Image source, PAris normandieRoger Collinge: As an ordinary citizen lucky enough to live in a country with free speech I join my name in support of this magazine and all who work for it with deepest sympathy to those who have suffered from this horror. Freedom of speech means what it says. It includes the right to be scurrilous and silly but it must remain. Those who oppose freedom of speech must be defeated.
Joachim: My thoughts are with Paris tonight. My pen will be firmly in the air.
The BBC's Security Correspondent Frank Gardner says that the Charlie Hebdo attack did not come out of the blue. It comes after a string of recent attacks, albeit less high-profile and resulting in fewer casualties.
Reuters is reporting more details on the three suspects being sought by French police. Officers are looking for two brothers in the Paris region and another man in the north-eastern city of Reims, according to the news agency. It quotes a government source as saying the two brothers are 32 and 34 years of age and the third suspect is 18 years old.
Le Monde reports, external that police sources have said that the three gunmen have been identified.
Caroline Wyatt, BBC Religious affairs correspondent has just posted this:
The killings at Charlie Hebdo are a deeply unwelcome reminder to the west that for some, mainly young radicalised men, their fundamentalist interpretation of their religion matters enough to kill those who offend it.
As a result, across western Europe, liberally-minded societies are beginning to divide over how best to deal with radical Islamism and its impact on their countries, while governments agonise over the potential for a backlash against Muslims living in Europe.
Today, mainstream Muslim organisations in the UK and France have unequivocally condemned the killings, saying that terrorism is an affront to Islam.
But the potential backlash, including support for far right parties and groups, may well hurt ordinary Muslims more than anyone else, leaving the authorities and religious leaders in western Europe wondering how to confront violence in the name of religion without victimizing minorities or being accused of "Islamophobia".
Caroline Wyatt's full piece can be read here: Europe's struggle with Islamism
The BBC's Paris correspondent Hugh Schofield says that France has just lived through "one of those days which remain engraved in the national memory".
He adds: "Today everyone can share in the common defence of French values...But how long this unity will last is another question.
"Soon there will be the discordant voices. On the one hand there will be those saying the real lesson of the attack is that France should drop its 'naivety' concerning Islamism in the banlieues.
"On the other side there will be those warning against what the French call l'amalgame - i.e. lumping all Muslims together and claiming that the problem resides somewhere with their religion."