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.