The World Health Organization (WHO) said on Thursday 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, reports the AFP news agency.

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

"We're just advising for a bit of moderation," he was quoted as having told a press conference in which the findings of two reviews of available evidence on aspartame were presented.

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.

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 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".

A second group, JECFA -- the Joint Expert Committee on Food Additives formed by the WHO and its fellow UN agency the Food and Agriculture Organization -- met in Geneva from June 27 to July 6 to evaluate the risks associated with aspartame.

It concluded that the data it evaluated indicated no reason to change the acceptable daily intake (ADI), established in 1981, of zero to 40 milligrams of aspartame per kilogram of body weight.

With a can of sugar-free soft drink typically containing 200 or 300 mg of aspartame sweetener, an adult weighing 70 kg would therefore need to consume more than nine to 14 cans per day to exceed the ADI, assuming no additional aspartame intake from other sources.

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

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