The Yarsan faith is one of the oldest in the Middle East.
Also known as Ahl-e Haqq (People of the Truth), it is estimated to have about three million followers in Iran, most of whom live in western, predominantly Kurdish provinces. Another 120,000 to 150,000 live in Iraq, where they are commonly called Kaka'i.
Behnaz Hosseini, a visiting research fellow at the University of Oxford who has studied religious minorities in Iran and Iraq, recently spent time with a Yarsani community during a three-day period of fasting that takes place each autumn.
Photos courtesy of Behnaz Hosseini