A thick yellow fog shrouded the oil-rich provinces of Khuzestan and Bushehr, which border Iraq and are more than 400 kilometres (250 miles) from Tehran.

Buildings were barely visible in images carried by the official IRNA news agency, while residents protected themselves with masks.

In southwestern Iran, schools and public services will remain closed on Sunday, a working day, and all flights are suspended until further notice due to visibility having been reduced to 100 meters (330 feet), Tasnim news agency reported.

In the city of Abadan in Khuzestan province, the air quality was considered "hazardous" on Sunday, with an index of 500, exceeding by more than 25 times the pollution rates deemed acceptable by the World Health Organization (WHO).

The storm arrived from neighbouring Iraq, while another dust storm hit the city of Zabol in the southeastern Sistan-Baluchistan province, according to state TV.

Dust and sandstorms have long affected the region but have become more intense and more frequent in recent years, with Iran particularly hard hit.

Experts associate this trend with overgrazing, drought, deforestation and overuse of river water.

In September 2023, at least three people died, and more than 1,300 others required medical attention as dust storms swept across Sistan-Baluchistan province.

Iran, with a population of more than 85 million, is among the countries most vulnerable to climate change and the rise in global temperatures.

It has also endured repeated droughts as well as regular flooding, a phenomenon made worse when torrential rain falls on sun-baked earth.