Genetically modified foods currently on the market are unlikely to present new risks for humans, the UN's health agency said while urging a more cautious approach to future GM products.

The World Health Organisation (WHO) insisted in a study that procedures for checking new food products and genetically modified organisms needed to be adapted regularly to fast-paced change and innovation in the biotechnology industry.

Public perceptions or social concerns about the costs and benefits of GM foods must also be taken more seriously, the study said.

More international harmonisation was necessary to prevent a "genetic divide" forming that could deprive more sceptical nations of acknowledged production or nutritional benefits of some GM foods, according to the WHO.

"GM foods currently available on the international market have undergone risk assessments and are not likely to present risks for human health in any other form than their conventional counterparts," the study said.

No health problems had been found so far, it added.

International guidelines for assessing the risk of GM foods, which are governed by the WHO and the UN's Food and Agriculture Organisation (FAO) were "adequate" for measuring the safety of current GM produce, the study found.

However potential risks should be assessed on a "case-by-case" basis, taking into account the individual characteristics of each new genetically modified organism or foodstuff.

The study acknowledged gaps in current knowledge, notably over the issue of food allergies.

"A better understanding of the impact and interaction of food with the immune system is required to decipher how and whether conventional and GM foods cause specific health and safety problems," it said.

The three-year study was compiled by ten national regulators and experts with the WHO's food safety department, to try to establish an international "knowledge base" for the evaluation of biotechnology in food production.

It followed widespread concerns or doubts in recent years about the sale of food made from genetically engineered crops such as wheat, maize, tomatoes and potatoes, and their possible long-term impact on health.

In 2002 several southern African countries rejected food aid from the United States because it included genetically-modified corn

The issue has also generated a trade dispute between the United States, where authorities have widely embraced GM foods, and the European Union, where a more cautious approach prompted a ban until earlier this year.

GM crops cover almost four percent of global arable land, according to the study.