"We are calling for the assassination of cartoonist Lars Vilks who dared insult our Prophet, peace be upon him, and we announce a reward during this generous month of Ramadan of $100,000 for the one who kills this criminal," the transcript on the website said.
In a half-hour audio file entitled "They plotted yet God too was plotting," Abu Omar al-Baghdadi also named rival insurgent groups in Iraq and promised new attacks, particularly against the minority Yazidi sect.
Blown out of proportion
The al-Qaeda leader upped the reward for Vilks' death to $150,000 if he was "slaughtered like a lamb" and offered $50,000 for the killing of the editor of Nerikes Allehanda, the Swedish paper that printed Vilks' cartoon of the Prophet Muhammad with a dog's body on August 19th.
Vilks said from Sweden he believed the matter of his cartoons had been blown out of proportion.
"We have a real problem here…we can only hope that Muslims in Europe and in the Western world choose to distance themselves from this and support the idea of freedom of expression."
Ulf Johansson, editor in chief of Nerikes Allehanda, said he took the bounty "more seriously" than other threats he had received. "This is more explicit. It's not every day somebody puts a price on your head."
Johansson said he had contacted the police and that they had already started work on the threat.
Aside from a few scattered protests and condemnations by Muslim countries, the reaction to the cartoon has been muted, in contrast to last year's fiery protests that erupted in several Muslim countries after a Danish newspaper published 12 cartoons of Muhammad that were reprinted in a range of Western media.
Freedom of the press
In an attempt to defuse the tensions caused by the cartoon in both Sweden and abroad, Swedish Prime Minister Fredrik Reinfeldt invited 22 Sweden-based ambassadors from Muslim countries to talk about the sketch last week.
Reinfeldt expressed regret at the hurt it may have caused, but said that according to Swedish law it is not up to politicians to punish the free press.
Al-Baghdadi added in his message that if the "crusader state of Sweden" didn't apologize, his organization would also attack major companies.
"We know how to force you to retreat and apologize and if you don't, wait for us to strike the economy of your giant companies including Ericsson, Scania, Volvo, Ikea, and Electrolux," he said.
No photo has ever appeared of al-Baghdadi, whom the US describes as a fictitious character used to give an Iraqi face to an organization dominated by foreigners. The US has said that, under interrogation, a top al-Qaeda member revealed that al-Baghdadi's speeches are read by an actor.
Al-Qaeda in Iraq in the past has carried out operations in Jordan and may have links to militant groups in Lebanon, but is not known to have any kind of presence in Europe.