TEHRAN -- President Mohammad Khatami here Saturday blamed cars as the biggest air pollutants in Iran with its capital Tehran listed among the world's most polluted cities.

He stressed the government's determination to standardize fuel for new cars and those on the streets.

"From now on, all the Iranian-made cars will be provided with favorable standards for fuel consumption," Khatami told reporters in a day which is marked nationwide as a Clean Air Day'."

Iran will start presenting lead-free gasoline throughout the country in the coming days and increase car checkup centers, he added.

The Iranian president also praised former Tehran mayor, Gholamhossein Karbaschi, who was removed from post on charges of graft in the city hall and remanded in jail for a while before being granted amnesty by Leader Ayatollah Ali Khamenei.

"If the municipality's plans on expanding greenery and traffic flow had not been implemented during Mr. Karbaschi's tenure, Tehran would have choked now under very difficult situation," Khatami said.

He described environmental hazards among the most serious concerns of the world and that of Iran.

He asked Iranians to cooperate with the government on improving the country's environmental situation so that the psychological and physical security of the residents and their children is guaranteed.

Vice-President and the Head of the Department of Environment, Ma'soumeh Ebtekar, said that most of the cars produced currently in Iran meet environmental safety standards.

She blamed 50 percent of the air pollution in Tehran on diesel-fueled cars which, she said, constitute only 10 percent of the cars on the capital's streets.

Out of every 100 families in the 12-million city, some 42 have cars and more than 92 percent use them for work or other trips.

Meanwhile, children in Iranian cities held rally to protest against air pollution.