"A European citizen was detained in the city of Boroujerd as he was participating in the demonstration and leading the insurgents," Hamid Reza Abolhasani said as quoted by Tasnim news agency.
The Iranian official did not clarify which country the detainee was from.
Since December 28, several large Iranian cities have seen a number of protests over quality of life. At least 20 people have reportedly been killed so far, and 450 people have been detained.
Iranian President Hassan Rouhani said Monday that the unrest had been provoked by a mix of existing domestic problems and outside influence.