British-educated author Salman Rushdie, once subject to death threats over a depiction of the Prophet Mohammed, has spoken of his anger that 12 murdered Charlie Hebdo cartoonists have been "vilified and called racists".

Mr Rushdie, whose 1988 book The Satanic Verses prompted Iranian religious leaders to issue an edict calling for his death, made the comments following a speech at the University of Vermont in Burlington, in the US.

When asked by an audience member, he said: "The French satirical tradition has always been very pointed and very harsh, and still is, you know.

"The thing that I really resent is the way in which these, our dead comrades ... who died using the same implement that I use, which is a pen or pencil, have been almost immediately vilified and called racists and I don't know what else."

Mr Rushdie, who was born in India before being educated in the UK, added he felt free speech could not be limited, even if it caused offence.

"Both John F Kennedy and Nelson Mandela use the same three-word phrase which in my mind says it all, which is, 'Freedom is Indivisible'," the New York resident said.

"You can't slice it up, otherwise it ceases to be freedom. You can dislike Charlie Hedbo. But the fact that you dislike them has nothing to do with their right to speak."

While the religious edict was officially lifted in 1998, security at the event was reported to be heightened.