A French magazine editor has defended their decision to print caricatures satirising the Prophet Muhammad.
"Charlie Hebdo must be veiled!" says the cover of the magazine
Two French Muslim groups are suing Charlie Hebdo magazine for defamation over the cartoons, printed a year ago.
Editor Philippe Val told the start of the case in a Paris court the cartoons were critiquing "ideas, not men."
The newspaper Liberation republished the cartoons on Wednesday in solidarity with the magazine.
The groups - Paris Mosque and the Union of Islamic Organisations of France - say the magazine "insulted people on the basis of religion" in a case seen as a test of free speech.
Muslims regard images of the Prophet Mohammed as blasphemous.
"If we no longer have the right to laugh at terrorists, what arms are citizens left with?" Mr Val asked.
"How is making fun of those who commit terrorist acts throwing oil on the fire?"
The trial is seen as a test of the boundaries of free speech in France
A lawyer for the magazine read a letter out from French presidential candidate Nicolas Sarkozy.
Mr Sarkozy noted he was often a target of the magazine but said he would prefer "too many caricatures to an absence of caricature".
But the Muslim groups said Charlie Hebdo's decision to publish the cartoons "was part of a considered plan of provocation aimed against the Islamic community in its most intimate faith".
It was "born out of a simplistic Islamophobia as well as purely commercial interests".
The illustrations originally appeared in the best-selling Danish newspaper Jyllands-Posten on 30 September 2005 to accompany an editorial criticising self-censorship in the Danish media.
One image shows the Prophet Muhammad carrying a lit bomb in the shape of a turban on his head decorated with the Islamic creed.
Over the next few months they were reprinted in a number of French publications and elsewhere in Europe and around the world.
Reaction in the Muslim world built up in January and February of 2006 culminating in sometimes violent protests.
The two-day trial is being seen as a test of the boundaries of free speech and religious sensitivities in France.
In republishing the cartoons, Liberation called the trial "idiotic", adding: "It is not words which wound, or pictures that kill. It is bombs."
A television debate between Mr Val and Paris Grand Mosque rector Dalil Boubakeur proved an acrimonious affair.
Mr Boubakeur said the cartoons insulted all Muslims by suggesting they were all terrorists.
Mr Val said: "If we can't criticise religion anymore, there will be no women's rights, no birth control and no gay rights."
In October, a Danish court rejected a libel case brought by several Muslim groups against the Jyllands-Posten.
The court in Aarhus said there was not enough reason to believe the cartoons were meant to be insulting or harmful.