Kanpur was the most polluted city on the list, followed by Faridabad. Varanasi ranked 3rd, while Gaya was 4th. Delhi occupied the 6th spot.
Srinagar, Lucknow, Gurugram and Agra were some of the other cities that featured in the top 20. Bamenda in Cameroon, Peshawar, Rawalpindi, Kampala, Narayangonj and Doha were the six non-Indian cities on the list.
The ranking is based on the amount of fine particulate matter PM 2.5 in the air.
According to WHO, PM 2.5 contains pollutants that pose the greatest risk to health.
The report cited the Pradhan Mantri Ujjwala Yojana Scheme as an example to taking measures on controlling air pollution. WHO said, the scheme has enabled 37 million women living below the poverty line to switch to clean energy by providing them with free LPG connections.
Around 7 million people are killed due to air pollution across the world each year, WHO estimates show. Nine out of 10 people in the world breathe air containing large amounts of pollutants.
The report pointed out that most countries, especially high income countries, are taking action to lower air pollution from particulate matter.
"We are seeing an acceleration of political interest in this global public health challenge. The increase in cities recording air pollution data reflects a commitment to air quality assessment and monitoring," Dr Maria Neira, Director of the Department of Public Health, Social and Environmental Determinants of Health, at WHO was quoted as saying.
The South-East Asian and Eastern Mediterranean regions showed the highest levels of ambient air pollution.
