The WHO said on Friday it was now classifying aspartame, an artificial sweetener commonly used in soft drinks, as "possibly carcinogenic to humans" – though the acceptable daily intake level remains unchanged.

"We're not advising companies to withdraw products, nor are we advising consumers to stop consuming altogether," said Francesco Branca, the World Health Organisation's nutrition and food safety director.

"We're just advising for a bit of moderation," he told a press conference presenting the findings of two reviews of available evidence on aspartame.

The WHO's International Agency for Research on Cancer (IARC) carried out its first-ever evaluation of the carcinogenicity of aspartame at a meeting in Lyon, France, from June 6 to 13.

"The working group classified aspartame as possibly carcinogenic to humans," the WHO said.

It was placed in category Group 2B, based on the limited evidence available, which specifically concerned hepatocellular carcinoma – a type of liver cancer.

There was also limited-strength evidence regarding cancer in experimental animals.

Aspartame is an artificial chemical sweetener widely used in various food and beverage products from the 1980s onwards.

It is found in diet drinks, chewing gum, gelatin, ice cream, dairy products such as yoghurt, breakfast cereals, toothpaste, cough drops and chewable vitamins.

The Group 2B category also contains extract of aloe vera and caffeic acid found in tea and coffee, said Paul Pharoah, a professor of cancer epidemiology at the Cedars-Sinai Medical Center in Los Angeles.

"The general public should not be worried about the risk of cancer associated with a chemical classed as Group 2B," he said.

The IARC's Mary Schubauer-Berigan said the limited evidence for hepatocellular carcinoma came from three studies, conducted in the United States and across 10 European countries.

"These are the only epidemiological studies that examined liver cancer," she told reporters.

Branca added: "We have, in a sense, raised a flag here, indicating that we need to clarify much more the situation," but nor is it "something which we can dismiss." (AFP)