Iranian authorities have cracked down on a so-called "Instagram modeling ring," according to the head of Tehran's cybercrimes division, with eight people arrested and charges filed against another 21.

The arrests came after a two-year investigation uncovered more than 150 people "making and spreading immoral and un-Islamic culture and promiscuity," Javad Babaei said on state TV Sunday, according to AFP . The official said the authorities must "confront those who committed these crimes in an organized manner."

The eight arrested appeared on Instagram without a hijab covering their hair, a crime in the Islamic Republic. The two-year investigation – code named Spider II – focused on more than 300 popular Instagram accounts in the country, and authorities were able to identify 59 photographers and makeup artists, 58 models, 51 fashion salon managers and designers, and two organizations.

AFP said that the arrests were thought to refer to ones announced in March, when an official said eight models had been arrested for charges including "spreading prostitution and promoting corruption."

Instagram is popular in Iran, with more than 7.5 million users estimated in the country. It is one of the few Western social media platforms that are not blocked in the country.