A human chain of more than 500 people along the Zayandeh River in Isfahan was violently broken up by police and plainclothes forces.
The local website Saheb News reports that protesters were quickly swarmed by officers and forced to leave the area.
The report adds that at least two people were injured and seven to 10 were arrested.
The report indicates that security forces even beat a 45-year-old man carrying his child on his shoulders, which caused him to drop the child.
According to one participant in the human chain, it was meant to express environmental concerns about the river.
The Kaleme opposition website denounced the double standard used by police when protesters don’t have a permit. This refers to gatherings against the Rohani administration held earlier this month without any official permits; they were not confronted by police and there was no violent reaction by security forces.