Authorities in Iran claim to have foiled a terror by Sunni militants to bomb capital Tehran, according to the intelligence ministry.

The ministry said members of an "anti-Islamic terrorist takfiri group" had been arrested and explosives seized. Iranian state TV described it as "the biggest terrorist plot" to ever target Tehran.

State news agency Tasnim reported that terrorists planned "a series of bombing raids in several locations across the capital of Iran, specifically during the upcoming events in the holy month of Ramadan."

Iran uses the term 'takfiri' to describe Sunni extremists who condemn other Muslims as apostates who deserve death. It is a a derogatory term in both Arabic and Farsi.

The country is currently battling Islamic State (Isis) extremists in Syria, and has provided support to Shia militias battling the group in Iraq.

Sunni groups have committed terror attacks in recent years in the south-east of the country.

The intelligence ministry did not provide any information on the identity of those arrested.