Japanese police have arrested four people for selling obscene images created using generative AI in the first crackdown of its kind, a police spokesman and local media reports said Tuesday.

The four, who allegedly made posters and sold them online, "were arrested on Monday on suspicion of selling obscene images", a Tokyo police spokesman told AFP.

They sold them on auction sites several times last October, criminal acts for which they face up to two years in prison, fines of up to 2.5 million yen ($17,500), or both, he said.

Public broadcaster NHK and other media outlets said the suspects used free AI software to create images of naked adult women who do not exist in the real world.

They used prompts including terms such as "legs open".

The four, aged in their 20s to 50s, reportedly sold the posters for several thousand yen (around $20-50) each.

Tuesday's reports said the arrests were Japan's first for allegedly selling AI-created obscene images, which police could not immediately confirm.

Concern is growing worldwide over the use of AI for malicious purposes including through deepfakes, which turn genuine photos, video or audio of people into false likenesses.

Around 96 percent of deepfake videos online are non-consensual pornography, and most of them depict women, according to a 2019 study by the Dutch AI company Sensity.