Iran has announced Wednesday and Thursday this week will be public holidays because of "unprecedented heat" and told the elderly and people with health conditions to stay indoors, Iranian state media reported.
Many cities in southern Iran have already suffered from days of exceptional heat. State media reported temperatures had this week exceeded 123 degrees Fahrenheit (51 Celsius) in the southern city of Ahvaz.
Government spokesman Ali Bahadori-Jahromi was quoted by state media as saying Wednesday and Thursday would be holidays, while the health ministry said hospitals would be on high alert.
Temperatures are expected to be 39 C in Tehran on Wednesday.
Heatwaves have affected large parts of the globe in recent weeks. Scientists have linked them to human-induced climate change.