Junk food ads account for two-thirds of televised advertisements for food that are shown when children are likely to be watching, researchers into obesity said Friday, based on a study of 11 countries.

Germany and the United States led the way at 90 percent, with Britain and Australia the lowest at about 50 percent, the researchers said, urging governments to limit such marketing in order to combat obesity.

"Internationally, children are exposed to high volumes of unhealthy food and beverage advertising on television," Bridget Kelly, a nutrition researcher at the Cancer Council NSW in Australia, and colleagues told the European Congress on Obesity in Amsterdam.

"Limiting this food marketing is an important preventative strategy for childhood obesity."

About 177 million children and teenagers under 18 years old worldwide are clinically overweight or obese. The figures include 22 million overweight children under five years old, according to the International Obesity Task Force.

Obesity raises the risk of conditions like heart disease and type 2 diabetes, and the growing epidemic is piling pressure on many cash-strapped national health systems.

Unhealthy lifestyles including high-calorie diets, poor exercise and hours spent in front of the television or computer have contributed to the surge in childhood obesity.

"There is a lot of attention on unhealthy food marketing as an influence on childhood obesity and a lot of governments are reluctant to regulate," Kelly said in an interview. "So most countries in the study don't have regulations on food advertising."

The researchers, who looked at children in Australia, Asia, Eastern and Western Europe and North and South America, found that junk food ads mainly featuring fast food, confectionery and high-fat dairy foods increased during times young people were most likely to be watching.

"Children see around 4,000 to 6,000 food advertisements on television a year and between 2,000 and 4,000 are for unhealthy foods," Kelly said. "So even if you are in countries that are advertising less to children, that is still a lot."

While establishing a direct link between advertising and obesity is difficult, it is clear marketing plays a big role in the kinds of food children prefer, the researchers said.