Police in the southwestern town of Almendralejo have received 11 complaints from victims, all minors, a local police spokeswoman told AFP.

The alleged perpetrators of these images "manipulated photos of underage girls" to place their faces on images of naked "bodies of other people", she added. Some suspects have already been identified.

The fake nudes were generated using an AI app that is capable of producing very realistic photo montages, a police source said.

Spanish media said around 20 girls may have been victim of these manipulated photos.

Miriam Al Adib, the mother of a 14-year-old victim, said: "This is very serious".

"When I came home, one of my daughters, who was really upset, told me: 'look what they did'. It turns out they took a photo of her and they made it seem as if she was naked with the aid of artificial intelligence," she wrote on Instagram.

"Girls, don't be afraid to report such acts. Tell your mothers. Affected mothers, tell me, so that you can be in the group that we created."

Police told her the photos may have been distributed on OnlyFans, an online subscription platform known for adult content, or on pornographic sites, she added.

Another mother told Spanish public television TVE the fake nudes were used to try to blackmail her daughter, with the alleged creators of the images demanding money not to distribute them.

AI is causing growing concern around the world because the technology can be used for malicious purposes such as the creation of so-called "deepfakes" -- computer-generated, often realistic images and video, based on a real template.

Some 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.