The health risks could be eliminated and some 1.5 million lives saved if people in the world's poorest countries were able to give up solid fuels, the WHO said in a statement.

Reliance on solid fuels and indoor air pollution is rated as one of the 10 most important threats to public health, causing pneumonia and crippling respiratory disease.

About three billion people depend on wood, dung, crop residues and coal for cooking and heating.

"The prevention potential is enormous," said WHO Assistant Director-General Susanne Weber-Mosdorf.

"Solutions are available, and it is our international responsibility to promote the health and well-being of those affected, who are mostly women and children," she added.

The WHO is calling for a shift towards cleaner and more efficient modern fuels, such as biogas, Liquefied Petroleum Gas (LPG) and kerosene as well as improved cooking stoves, and smoke hoods to cut indoor household pollution.

The data was released as ministers met during the United Nations Commission on Sustainable Development in New York, to decide on measures against indoor air pollution.

The 21 worst-affected countries include 19 in sub-Saharan Africa, as well as Afghanistan and Pakistan. Last year, the WHO estimated that the death toll from "the killer in the kitchen" included 800,000 children and 500,000 women.

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