Tehran's deputy prosecutor Reza Jafari said 50 Iranians had been arrested and were under investigation for running such websites and promoting prostitution, according to Iran newspaper Vatan Emrouz.
He also said the term "corrupt on Earth" was appropriate to describe "a person who manages many immoral, anti-religious and anti-revolutionary sites, and corruption on Earth is legally punishable by death" under strict Islam.
Jafari, who is the prosecutor for a special tribunal against cybercrimes, said 90 websites had been shut down since March and that half of the 50 people arrested were out on bail. Iranian officials arrested 26 adult site operators last week.
The websites contained pornographic material including "incest, sex with children and animals, homosexuality and erotic stories" as well as "insults to religious sanctities," Jafari said.
In March, representatives of Iran's Revolutionary Guards said it had launched a crackdown on several groups who had set up anti-Islamic and pornographic sites on the Internet.
The websites were not named but the Revolutionary Guards accused Internet search engine Google and rival firms of "offering financial support" to the unidentified groups.