Seven million people died as a result of air pollution in 2012, the World Health Organization estimates.
Its findings suggest a link between air pollution and heart disease, respiratory problems and cancer.
One in eight global deaths were linked with air pollution, making it "the world's largest single environmental health risk", the WHO said.
Nearly six million of the deaths had been in South East Asia and the WHO's Western Pacific region, it found.
The WHO said about 3.3 million people had died as a result of indoor air pollution and 2.6 million deaths were related to outdoor air pollution, mainly in low- and middle-income countries in those regions.
'Heavy price'
WHO public health, environmental and social determinants of health department director Dr Maria Neira said: "The risks from air pollution are now far greater than previously thought or understood, particularly for heart disease and strokes.
"Few risks have a greater impact on global health today than air pollution.
"The evidence signals the need for concerted action to clean up the air we all breathe."
Reducing air pollution could save millions of lives, said the WHO.
WHO family, woman and children's health assistant director-general Dr Flavia Bustreo said: "Cleaning up the air we breathe prevents non-communicable diseases as well as reduces disease risks among women and vulnerable groups, including children and the elderly.
"Poor women and children pay a heavy price from indoor air pollution since they spend more time at home breathing in smoke and soot from leaky coal and wood cook stoves."
'Robust and accurate'
The WHO assessment found the majority of air pollution deaths were linked with cardiovascular diseases.
For deaths related to outdoor pollution, it found:
- 40% - heart disease
- 40% - stroke
- 11% - chronic obstructive pulmonary disease (COPD)
- 6% - lung cancer
- 3% - acute lower respiratory infections in children
For deaths related to indoor pollution, it found:
- 34% - stroke
- 26% - heart disease
- 22% - COPD
- 12% - acute lower respiratory infections in children
- 6% - lung cancer
University of Birmingham professor of environmental and respiratory medicine Jon Ayres said the review needed to be taken seriously.
"The estimates for the impact of outdoor air pollution are robust and as accurate as can be developed at the moment," he said.
The WHO estimates were based on:
- satellite data
- ground-level monitoring
- modelling how pollution drifts in the air
- pollution-emissions data
- more
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