The Cartooning for Peace group said cartoonists were increasingly becoming the victims of repressive crackdowns on free speech.
The watchdog's first annual global report also documents attacks on freedom of expression in Kenya, Venezuela, Egypt, Malaysia, Jordan, Ecuador and Burkina Faso.
Its founder, the French cartoonist Plantu -- who set up the group a decade ago with former United Nations chief Kofi Annan -- told AFP that his peers were in danger across the globe.
Cartoonists were the canary in the mineshaft, he said, "often the first to be threatened" by authoritarian governments.
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"For six years we have been trying to defend the cartoonist Rayma," who was first targeted by Hugo Chavez and has since fled to Florida after being threatened by his successor, President Nicolas Maduro.
The report also highlights the case of Turkish cartoonist Musa Kart, who has been jailed since October with colleagues from the liberal daily Cumhuriyet on accusations of "collusion with a terrorist organisation".
The newspaper incurred the wrath of Turkish President Recep Tayyip Erdogan for running a story about a shipment of arms intercepted at the Syrian border, allegedly bound for Islamic extremists.
It said the Malaysian cartoonist Zunar has been subject to nearly a decade of persecution, travel bans and harassment for his work criticising official corruption.