But police chief Esmaeel Ahmadi Moghaddam stressed that the 500 figure did not represent the total number of people arrested during Sunday's Ashura rituals as other security agencies had also detained protesters.
"On that day, 500 of the rioters were arrested and after investigating their cases, 300 are still held by the police," the official IRNA news agency quoted Ahmadi Moghaddam as saying.
"Not all the arrests were carried out by the police, and other entities like the ministry of intelligence and Basij (Iran's volunteer militia) have also arrested rioters, so the final count will be announced later."
Ahmadi Moghaddam said that 120 police were wounded during the opposition protests, of whom 60 remained in hospital.
The Iranian authorities have said that eight people died during Sunday's protests but have rejected opposition charges that they were killed by security forces, insisting the deaths were "suspicious."
The police chief said that his officers would now adopt a policy of zero tolerance.
"The police had tolerated the rioters before Ashura, but now that the rioters have shown their allegiance to movements trying to topple the regime, there will be no more tolerance and they will be dealt with severely," he said.
"Some of those who were arrested before were dealt with with tolerance and were freed.
"But we will not tolerate those arrested on Ashura day and they will not be released until the investigation into their cases has been completed."
The government called on its supporters to hold nationwide rallies on Wednesday to show their condemnation of the opposition demonstrators' "desecration" of Ashura.
