Iranian media report that schools, universities, and government offices will be closed in the capital, Tehran, on December 4-5 because of high air pollution.
State news agency IRNA quoted Tehran Governor Morteza Tamadon as saying hospitals and banks would remain open, but he recommended that residents avoid unnecessary travel.
Pollution caused mainly by vehicle fumes has been on the rise in the past few days in Tehran and some other big cities.
Tehran's situation is the worst because it is wedged between two mountains, where polluted air becomes trapped.
Tehran authorities often order the closure of schools and government offices in autumn, when high pollution levels cause health problems.
Based on reporting by AFP and dpa