GENEVA (Reuters) - The World Health Organisation, which has been championing an international campaign against tobacco use, called on Tuesday for a global ban on smoking at work and in enclosed public places.

The U.N. health agency said it would help limit non-smokers' exposure to second-hand smoke, which can kill through heart disease and serious respiratory and cardiovascular illness.

"The evidence is clear, there is no safe level of exposure to second-hand tobacco smoke," said WHO Director-General Margaret Chan in a statement ahead of World No Tobacco Day on Thursday.

"Many countries have already taken action. I urge all countries that have not yet done so to take this immediate and important step to protect the health of all," she said.

A number of European Union countries, including France, Spain, Ireland and Portugal, are amongst those to have already introduced such bans.

The Geneva-based agency said its recommendation was based on three studies on second-hand smoke, two made in the United States and one by the International Agency for Research on Cancer.

According to the WHO, some 200,000 workers die each year due to exposure to smoke at work, while around 700 million children, around half the world's total, breathe air polluted by tobacco smoke, particularly in the home.

The agency says that tobacco is the leading cause of preventable deaths worldwide. The number of smokers continues to rise rapidly in developing countries.

Member countries of an international treaty against smoking, the WHO-backed Framework Convention on Tobacco Control, are due to discuss guidelines on exposure to second-hand smoke at a meeting in Bangkok starting on June 30.