This is an "act against the fundamental values of modern civilisation that must be condemned in the strongest terms by the entire free and peace loving world," Pahor said in a letter of condolences sent to French President Francois Hollande.

Prime Minister Miro Cerar tweeted his "strong condemnation of the outrageous terrorist act against Charlie Hebdo, which targeted the freedom of the media, one of the key civilisational achievements".

In a second tweet, he said: "As the prime minister I express Slovenia's full solidarity with France, the media, and the families of the victims."

Foreign Minister Karl Erjavec also condemned the attack, saying it showed how relative security is, a reminder that "we have to promote peaceful policies through dialogue".

The attack is "yet another warning that we have to be utterly cautious and that the international community may not allow these kinds of terrorism," he said on the margins of a consultation of Slovenian diplomats.

Erjavec also expressed condolences to the families of the victims.

Media reports suggest at least 12 people were killed and four injured when two masked attackers opened fire in the offices of the paper, known for its persistent satirising of Islam.