The weather is causing health problems across the region
Many offices, businesses and education establishments in Iran have closed for two days because of high pollution levels caused by desert storms.
State television said air pollution in the capital, Tehran, had reached levels not seen for 30 years.
Visibility has been reduced to several hundred metres, while some domestic flights have been cancelled.
The elderly, children and people with heart and respiratory problems have been told to stay indoors in west Iran.
"All administrative offices are closed because of the atmospheric pollution which has soared several times higher than the normal threshold," said Tehran governor Morteza Tamadon on state television.
In neighbouring Iraq, officials described the last week of sandstorms as the worst in history. Hundreds of people were taken to hospital with respiratory problems.
Reports say a reduction in the flow of the once-mighty Tigris and Euphrates rivers - from drought and upriver damming - has aggravated the situation.