Heavy snowfall has caught residents of the Iranian capital Tehran off guard, bringing the city to a standstill and closing schools in the northern districts of the metropolis.

It all began with tiny hailstones hitting northern part of Tehran during Saturday morning rush hour but it soon grew into a full force snowfall and blanketed the streets.

The snow resulted in heavy traffic in many streets as it covered the city with a blanket of 30 centimeters.

Hamid Mousavi, mayor of Tehran's first district, told the Iranian Students News Agency (ISNA) that the backed-up traffic prevented the use of snowploughs and forced the municipal workers to clear roads and pavements by hand.

Snowing is a rare occurrence in Tehran during the fall. It came following days of windless weather that pushed air pollution dangerously high.

Forecasters have predicted a ground frost and a sharp drop in temperature for the coming days.

All elementary schools in and around the Iranian capital were suspended on Wednesday, the last day of the education week, amid elevated levels of pollution in the smog-ridden city.

Anoushirvan Mohseni, governor of Tehran Province, said that elementary schools in the cities of Tehran, Varamin, Qarchak and Pishva, all to the south of the capital, were closed on Wednesday as an index measuring the quality of the air in those cities was at unhealthy levels, especially for sensitive groups of the population.