GENEVA, Sep 22 (AFP) - The World Health Organization strengthened its air quality guidelines on Wednesday (Sep 22), saying air pollution was now one of the biggest environmental threats to human health, causing seven million premature deaths a year.

Urgent action is needed to reduce exposure to air pollution, said the UN body, ranking its burden of disease on a par with smoking and unhealthy eating.

"WHO has adjusted almost all the air quality guideline levels downwards, warning that exceeding the new ... levels is associated with significant risks to health," it said.

"Adhering to them could save millions of lives."

The guidelines aim to protect people from the adverse effects of air pollution and are used by governments as a reference for legally binding standards.

The UN health agency last issued air quality guidelines, or AQGs, in 2005, which had a significant impact on pollution abatement policies worldwide.

In the 16 years since however, the WHO said more evidence had emerged showing that air pollution effected health at lower concentrations than previously understood.

"The accumulated evidence is sufficient to justify actions to reduce population exposure to key air pollutants, not only in particular countries or regions but on a global scale," the organisation said.