Almost 400 people have been hospitalised with heart and respiratory problems caused by heavy air pollution in Tehran, with nearly 1,500 others requiring treatment, an official said Tuesday.

Year round, more than four million cars spew exhaust fumes into the atmosphere of the Iranian capital. The situation worsens in winter, when cold air leads to a carcinogenic fog that blankets the city.

The latest casualties were treated Monday, according to Hassan Abbas, an emergency services manager quoted by the official IRNA news agency.

"Some 392 people were admitted to hospital due to respiratory and heart problems," he said. "We treated another 1,434 externally."

Authorities are said to be considering school closures and the introduction of traffic restrictions for the whole capital Wednesday, although this has not yet been officially confirmed.

However, the sick and elderly have been asked to avoid city traffic due to the effects of breathing in a noxious mix of carbon monoxide, sulphur dioxide, nitrogen oxide and dirty rubber particles.

The capital and other cities, including top tourist attraction Isfahan and the religious destination of Mashhad,have experienced pollution peaks in recent weeks.

Tehran, with its population of 12 million people, is one of the most polluted cities in the world, partly because of an altitude ranging from 1,100-1,700 metres (3,600-5,600 feet) above sea level in a basin surrounded by mountains.

In addition, Iranian cars consume on average more than other countries, a situation made worse by some fuel being of low quality.

Pollution peaks in winter are regularly caused by the climate inversion phenomenon, where cold air near the ground is trapped by warmer air above preventing pollution being dispersed over a bigger area.

In 2012, pollution contributed to the premature deaths of 4,500 people in Tehran and about 80,000 in the country, according to the health ministry.