More than 1.7 million children under the age of five are being killed each year by the polluted environment, according to two reports by the World Health Organization published on Monday.

The factors that cause the death of more than one-in-four children under five include air pollution, unsafe water and lack of sanitation.

Margaret Chan, the director-general of the WHO said: "A polluted environment is a deadly one – particularly for young children. Their developing organs and immune systems, and smaller bodies and airways, make them especially vulnerable to dirty air and water."

The effects of pollution can begin during pregnancy and increase the risk of premature birth. Later, air pollution increases the incidence of pneumonia and asthma as well as longer-term illnesses such as cancer and heart disease.

In the report, Don't Pollute my Future! The Impact of the Environment on Children’s Health, released on Monday, authors break down the numbers of child deaths per environmental factor.

? 570 000 children under five die from respiratory infections, such as pneumonia.

? 361 000 children under five die due to diarrhea, from unsafe water, poor sanitation and hygiene.

? 270 000 children die during their first month of life from conditions including being born prematurely, which could be prevented by improved environmental conditions.

In the second report, Inheriting a Sustainable World: Atlas on Children’s Health and the Environment, the authors argue that most of the 1.7 million deaths could be prevented by using clean cooking fuels and improving sanitation.