NEW DELHI- India today rejected the findings of a World Health Organization (WHO) study that ranks New Delhi as the world's worst city for air pollution , with government scientists saying the U.N. agency had overestimated levels in the capital.

A WHO study of 1,600 cities released on Wednesday found air pollution had worsened since a smaller survey in 2011, putting city-dwellers at a higher risk of cancer, stroke and heart disease.

The study found New Delhi to have the dirtiest air , with an annual average of 153 micrograms of small particulates.

"Delhi is not the dirtiest , certainly it is not that dangerous as projected," said A.B. Akolkar, a member secretary of the Central Pollution Control Board of India .

One health advocacy group welcomed the WHO study, however, saying it should spur the Indian government to tighten up fuel emission standards. Growing traffic on city streets is a major cause of air pollution .

India 's Centre for Science and Environment (CSE) said the government should respond by setting an ambitious agenda to reduce toxic risks in Asia's third-largest economy.