(reuters) -- State TV said schools, closed since Sunday, would remain closed on Wednesday in Tehran, which has a population of 14 million and more than 8 million cars and motorbikes.

To reduce the pollution, Iranian authorities announced on Monday that cars were only allowed on the roads on alternate days, depending on their number plates. Mines and cement factories have been closed in Tehran province.

Schools in the northwestern cities of Tabriz and Urmia and the central city of Isfahan also have been closed because of the high pollution level, Iran's state news agency IRNA reported on Tuesday.

Residents shared on social media pictures of Tehran covered with a blanket of smog.

The capital has been experiencing an alarming level of air pollution since Sunday but despite reduced traffic, it has remained high in the city, which sprawls at the foot of the Middle East´s highest mountains.

Iran's Health Ministry has called on the elderly, children, and people with heart problems to stay at home. Iranian media reported that a growing number of people with severe breathing difficulties have been hospitalised.

Iranian media gave no specific reason for the increased pollution, which comes after a similar incidence in 2014 that left some 400 people needing hospital treatment.