Outdoor air pollution is the leading cause of cancer, a World Health Organisation (WHO) agency has revealed.

The International Agency for Research on Cancer (IARC) said that in 2010, 223,000 deaths from lung cancer worldwide resulted from air pollution, also pointing out there was also convincing evidence it increases the risk of bladder cancer.

Air pollution, mostly caused by transport, power generation, industrial or agricultural emissions, and residential heating and cooking, is already known to raise risks for a wide range of illnesses including respiratory and heart diseases.

Kurt Straif of the IARC said "The air we breathe has become polluted with a mixture of cancer-causing substances. We now know that outdoor air pollution is not only a major risk to health in general, but also a leading environmental cause of cancer deaths".

Research suggests that in recent years, exposure levels have risen significantly in some parts of the world - particularly countries with large populations going through rapid industrialisation such as China.

In a statement the IARC said both outdoor air pollution and "particulate matter" would not be classified among its Group One human carcinogens.

That puts them alongside more than 100 other known cancer-causing substances including asbestos, plutonium, ultraviolet radiation and tobacco smoke.

IARC director Christopher Wild said the decision to classify outdoor air pollution as carcinogenic was an important step to alerting governments to its dangers and potential costs.

He said "There are effective ways to reduce air pollution and, given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action".