TEHRAN, Iran — Iran has launched a new crackdown on social media, arresting fashion models active on photo-sharing websites and a blog website manager after Tehran's top leader declared war on un-Islamic thoughts on the Internet.

Eight members of a modeling network were arrested and accused of publishing photos of women without the obligatory hijab headscarf on the picture-sharing application Instagram, Tasnim news agency said on Sunday.

State television also broadcast live "confessions" of a model who explained she posted photos of herself on Instagram wearing certain clothes or beauty products to earn money through advertisements.

The semi-official student news agency ISNA also reported on Monday the arrest of Mehdi Butorabi, 53, the manager of the popular Persian Blog launched in 2001 as the Iranian equivalent of the Blogger weblog publishing tool.

It provided a vibrant, diverse platform for thousands of young Iranians to express their thoughts.

The Center for Investigation of Organised Crime, a branch of the elite Revolutionary Guards Corps (IRGC), monitors social media to hunt for evidence of immorality or subversion.

Iran blocks access to Facebook, Twitter and YouTube but millions of Iranians easily get around that by using virtual private networks (VPNs).

However, that does not make them immune from state surveillance. Last year, three men and three women who posted a video of themselves singing and dancing along with a Western pop song were arrested.

Iran's Supreme Leader Ayatollah Ali Khamenei said on Saturday the Internet was promoting un-Islamic thoughts that should be promptly dealt with.

"This is a real battlefield. The clerics and seminary students should prepare to enter this field and fight against deviations and erroneous thoughts," Khamenei was quoted as saying by his website.

By Bozorgmehr Sharafedin; editor: Tom Heneghan.