Iran's semi-official ISNA news agency says authorities have detained several organizers of a gathering marking the birth of the pre-Islamic King Cyrus the Great, the founder of the Achaemenid Empire.

Monday's report cites Fars province prosecutor Ali Salehi as saying the activists were detained because of "norm-braking and anti-values" slogans that were chanted during a gathering last week. Salehi did not elaborate on the number of detainees.

At the gathering, many admired Cyrus as the founder of the First Persian Empire and demanded freedom of thought, according to social media posts.

Every October Iranians gather to celebrate at Cyrus' tomb in the town of Pasargad, some 500 miles (800 kilometers) south of Tehran.

Clerics who came to power after the 1979 Islamic Revolution generally reject the celebration of pre-Islamic icons.