Children have been used as 'lab rats' in GM rice trials that were carried out in breach of ethics rules drawn up in response to the medical crimes of Nazi Germany, it is claimed.
Youngsters aged 6-10 were fed so-called Golden Rice, which has been modified to contain enhanced levels of beta carotene or vitamin A.
The rice is being developed to combat Vitamin A deficiency, which is linked to damage to the sight, poor brain development and immune system failure.
However high consumption can also have harmful toxic effects and cause birth defects.
Critics are furious that the GM rice was not put through animal feeding trials to ensure it was safe before being given to children.
The decision to use the children has been condemned as 'completely unacceptable' by a group of 22 scientists - all GM critics - from Britain and around the world.
They claim it is indicative of moves by the biotech lobby, led by the USA and biotech firms, to force GM food into the mouths of the world without proper assessment.
The project was financed and run through the US National Institutes of Health and involved children in China and America.
The scientists have written an open letter to the team behind the experiments, condemning the way they were conducted.
It states: 'We are writing to express our shock and unequivocal denunciation of the experiments being conducted by your colleagues which involve the feeding of genetically modified Golden Rice to human subjects.'
The letter says there has been 'woefully inadequate pre-clinical evaluation' of the rice.
The scientists argue there is a large body of evidence showing GM food production can trigger gene mutations which 'can result in health damaging effects when GM food products are fed to animals'.
The letter adds: 'Our greatest concern is that this rice, which is engineered to overproduce beta carotene, has never been tested in animals'.
It says there is evidence that certain chemicals derived from beta carotene 'are both toxic and cause birth defects'.
Critics of the GM experiments says the Nuremburg code states that children under 10 are not considered legally capable of giving consent to participation in such experiments.
They say the code also requires that human guinea pigs should not be used if scientists have an alternative experimental method.
Thirdly, experiments on humans should not be conducted until tests with animals have identified potential hazards.
Among the leading bodies behind the GM Golden rice project are the biotech company Syngenta, the Rockefeller Foundation and the charitable foundation set up by Microsoft boss Bill Gates.
The list of signatories to the protest letter includes Malcolm Hooper, emeritus professor of medicinal chemistry at Sunderland University, who said: 'This type of experimentation is frightening - children as lab rats - it is not on.'
Another is Prof David Schubert, of the Salk Institute of Biological Studies, San Diego, who said: 'It is completely immoral to feed this rice to children without proper safety testing...It's like putting a new drug on the market with no toxicology or safety trials.'
Other signatories include Prof Carlo Leifert, director of the Tesco Centre for Organic Agriculture at Newcastle University; and Dr Stanley WB Ewen.
Dr Ewen was involved in rat feeding trials in Scotland in 1999 which linked GM potatoes to harmful toxic effects.
Dr Brian John, of GM Free Cymru said: 'These irresponsible and dangerous trials must be stopped immediately, and the Golden Rice Project team must put its much-vaunted product through a full and transparent testing process before it is allowed to pass the lips of any other human being.'
Project manager at the Golden Rice Organisation, Dr Adrian Dubock, denied that the Nuremburg Code has been breached. He said the feeding trials had been approved by independent ethical review panels.
'Parents were not given financial rewards for their children's participation - to avoid undue pressure on poor families - but children were rewarded with school bags and pencils and paper as a thank you for participating,' he said.
Dr Dubock said 6,000 people around the world die every day due to illnesses related to failing immune systems where Vitamin A deficiency is a factor.
'The Golden Rice contains the food colours found everywhere in coloured natural foods and the environment...There is no possible way the trials could do any harm to the participants.'
Dr Dubock said animal experiments would not have helped. 'As humans are the designed beneficiaries of Golden Rice, animal testing could not answer the questions posed,' he said.
This appears odd as all GM foods, which are designed to be eaten by humans, are required to go through animal testing by food safety authorities in many countries.