The arrests apparently began in the city of Kavar close to Shiraz where Sufis are reported to have come under attack from "plainclothes agents" and members of the Basij militia.
Opposition websites have reported that those who assaulted the dervishes were armed and they used tear gas.
Davood Montazeri, a lawyer member of the Gonabadi dervishes told Radio Farda that the Kavar incident took place after a cleric in Fars province, who he identified as “Shahbazi,” called on citizens to demonstrate against dervishes.
Radio Farda reports that Sufi shops were set on fire and their houses were attacked by a group of hardliners chanting “Death to American dervishes.”
Sources close to the dervishes have told Radio Farda that scores of dervishes were detained, apparently by security forces. A number are reported to have been injured.
“Majzooban121” which covers news related to the Gonabadi dervishes has posted several pictures of the injured.
Following the Kavar incident, a number of dervishes were arrested in other cities, including Tehran, the website reports.
Those arrested in the Iranian capital include at least one lawyer and several dervishes who worked with “Majzooban121.”
The website has posted the names and pictures of 11 of the detainees.
In recent years, Iranian authorities have demolished several houses of worship of dervishes in Qom, Isfahan and other cities.
Dervishes believe their growing popularity is one of the main reasons for the increased pressure.
The Nematollahi order is Iran's largest Sufi order, with reportedly over 2 million members across the country, including major cities such as Tehran and Isfahan.
-- Golnaz Esfandiari
Read more on the tensions between the Iranian establishment and Sufis here