Scientists say climate change amplifies extreme weather. File photo
"Twenty-one people were killed and two are still missing," in the floods that affected several towns in and around Estahban county in the southern province of Fars, Hossein Darvishi, provincial head of the Red Crescent Society, was quoted as saying by state TV.
Videos posted on local media and social media showed cars caught in the rising waters of the Roodball river and carried away while parents tried to rescue their children from the vehicles.
The governor of Estahban, Yousef Kargar, said "around 5pm yesterday, heavy rains... in the central parts of Estahban County led to flooding," according to state news agency IRNA.
Estahban is 174 kilometres (108 miles) east of the provincial capital Shiraz.
The tragedy happened on a summer weekend in Iran, when families tend to head to cooler areas such as riversides, lakesides and valleys.
In January two people were initially reported killed in flash flooding in Fars when heavy rains hit the area. File photo
"A number of local people and sightseers (from other areas) who had gone to the riverside and were present in the river bed were caught in the flood due to the rise in the water level," Kargar added.
Iran has endured repeated droughts over the past decade, but also regular floods, a phenomenon made worse when torrential rain falls on sun-baked earth.
Photos released by Iran's Red Crescent Society showed rescuers walking on cracked dry soil while others worked among reeds.
In 2019, heavy inundations in the country's south left at least 76 people dead and caused damage estimated at more than $2 billion.
In January two people were initially reported killed in flash flooding in Fars when heavy rains hit the area, but the toll rose to at least eight there and elsewhere in Iran's south.
Scientists say climate change amplifies extreme weather, including droughts as well as the potential for the increased intensity of rain storms.