A semi-official news agency in Iran is reporting that an argument between supporters of hard-liners and reformists in the country escalated into a shooting that wounded four people during the country's runoff election.

The rare outbreak of violence Friday during the vote underlines the tension between the two camps as control of the Islamic Republic's parliament hangs in the balance.

The semi-official ISNA news agency quoted Hossein Zolfaghari, Iran's deputy interior minister for security, as saying the shooting happened in the city of Mamasani in Fars province.

He said: "Everything is calm in Mamasani now." He did not elaborate, but said police were searching for those responsible.

The country's parliamentary runoff elections is a key poll expected to decide exactly how much power moderate forces backing President Hassan Rouhani will have in the next legislature.