French prosecutors are investigating a cartoonist after a complaint he was distributing child pornography through his sexually explicit work.

Bastien Vives, 38, has long been a star of France's much-loved graphic novel scene and was due to be honoured at the Angouleme International Comics Festival later this month.

But protests and online outrage led the festival to drop him, saying there had been threats of violence against Vives and its staff.

Vives has been praised for books such as "A Sister" and "The Blouse" that included erotic elements, but were widely considered moving and sophisticated.

But other works include highly graphic scenes of sex involving children, which, despite absurdist storylines, have been accused of promoting or normalising paedophilia.

The authorities have opened cases against Vives and two publishing houses following complaints from a pair of NGOs, the Foundation for Childhood and Innocence in Danger, prosecutors said Friday.

These cartoons "show children represented in sexually explicit scenes that undoubtedly have a pornographic character," said one of the complaints.

It will now fall to prosecutors in Nanterre to decide where the line is drawn between art and illegal pornography.

Vives denies any pornographic intent in his work, saying they are part of a "burlesque, humouristic genre".

"At no time did I want to hurt victims of sexual crimes or abuse," he said in an apology posted on Instagram after he was dropped from the festival.