TEHRAN, Iran (AP) _ Iranian authorities have asked people suffering from heart and asthma problems to remain indoors after air pollution in the capital, Tehran, reached dangerous levels Wednesday, the Islamic Republic News Agency reported.

Authorities have also ordered kindergartens and elementary schools to remain closed Thursday and have imposed unspecified traffic restrictions.

The agency did not say how high pollution levels had reached.

Last year, several thousand schools were shut down after air pollution reached more than six times the acceptable level set by the World Health Organization.

The city's fleet of old cars emit noxious exhaust fumes. Most of the cars are more than 20 years old and according to official estimates, they account for 75 percent of Tehran's pollution.