The Taoiseach Enda Kenny says he is "shocked and appalled by the brutal and horrific killings" at the offices of the Charlie Hebdo magazine in Paris.
British Prime Minister David Cameron has described the murders of 12 people in Paris as “sickening”.
Condemning the attack on the French satirical weekly Charlie Hebdo, he said on Twitter: “We stand with the French people in the fight against terror and defending the freedom of the press.”
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
And he told MPs: “This House and this country stands united with the French people in our opposition to all forms of terrorism and we stand squarely for free speech and democracy.
“These people will never be able to take us off those values.”
President Barack Obama’s spokesman said US officials had been in close contact with the French authorities.
Josh Earnest told CNN the French have been “stalwart allies” in the US fight against Islamic State extremists, adding: “We know they are not going to be cowed by this terrible act.”
Germany's Chancellor Angela Merkel has said:: "We stand by our French friends in these difficult hours", while Spain's Prime Minieter Mariano Rajoy said: "My firm condemnation of the terrorist attack in Paris. My condolences and solidarity to the French people and the victims."
European Commission President Jean-Claude Juncker said he was ``profoundly shocked'' by the carnage.
In a statement released in French by the European Commission, he said: “I am profoundly shocked by the brutal and inhumane attack on the Charlie Hebdo premises.
“It is an intolerable act, a barbaric act that concerns us all, as humans, and as Europeans.
“My thoughts go out to the victims and their families. I wish to express, both personally and on behalf of the European Commission, our greatest solidarity with France.”
And Nato general secretary Jens Stoltenberg said: “I strongly condemn the terrorist attack at the office of the Charlie Hebdo magazine in Paris today.
“This was a barbaric act and an outrageous attack on press freedom.
“My thoughts are with the victims and their families.
“We stand in full solidarity with our ally France.
“All Nato allies stand together in the fight against terrorism. Terrorism in all its forms and manifestations can never be tolerated or justified.”
Campaigners Index on Censorship condemned the attack.
Index chief executive Jodie Ginsberg said: “The ability to express ourselves freely is fundamental to a free society.
“This includes the freedom to publish, to satirise, to joke, to criticise, even when that might cause offence to others. Those who wish to silence free speech must never be allowed to prevail.”