Air pollution has killed more than 3,000 people during one month in the Iranian capital, Tehran, according to a local official.
"Pollution has directly or indirectly caused the deaths of 3,600 people in the month of Aban [October 23 to November 23]," Mohammad Hadi Heydarzadeh, director of Tehran's clean air committee, said.
He said that the deaths were caused by heart attacks brought on by the pollution and that the smog was responsible for 80 per cent of the fatal heart problems in Tehran.
"It is a very serious and lethal crisis, a collective suicide," he said.
The new figures showed a sharp rise in pollution-related deaths in Tehran - 9,900 people were killed between March 2005 and March 2006.
Carbon monoxide from car exhausts is blamed for the majority of the deaths. 1.3 million ageing cars with poor fuel efficiency are causing respiratory and cardiac problems for the seven million residents of Tehran.
Half of Iran's six million cars fail to meet global standards and burn twice as much petrol as a European car. The low cost of petrol keeps the streets packed with cars and Tehran suffers severe traffic jams during rush hour.
"A real revolution is needed to resolve this problem," Heydarzadeh told Kargozaran newspaper.
The problem is particularly bad during the winter when a lack of wind and the cold air means that clouds of smog hang over the city for days on end.
The authorities regularly ask the elderly and children not to leave their homes, shutting schools to protect the pupils when the pollution is at its peak.