Environmental group Friends of the Earth has released a 51-page report, charging that 10 years after the first GM food appeared on supermarket shelves, biotech corporations have failed to prove its benefits for farmers or consumers.
The assessment was released to coincide with the opening of the first Conference of Parties to the Cartagena Protocol on Biosafety, a UN accord which came into force last September.
The US has not signed the protocol, which has been ratified by 86 countries and the European Union, but is lobbying hard for the acceptance of GM crops worldwide.
Tough EU laws
EU nations have infuriated the US by passing tough laws on identifying and labelling food that has GM ingredients - one of the major topics for debate at the conference.
Britain has already made it clear that London plans to take a firm stand.
Environment Minister Elliot Morley told AFP before the conference: "The US has to understand there is enormous sensitivity about genetically-modified food.
The US has also to understand we would not give blanket approval (to GM food products). There is no chance of that whatsoever."
"The reality of the last 10 years is that the safety of GM crops cannot be ensured, they are neither cheaper nor higher quality and they are not the magical solution to solve world hunger."
Friends of the Earth spokesman
"The bottomline must be consumer choice," said Morley. "We do have a number of GM food ingredients which are approved in the UK and they must be labeled and that will be extended to any GM products."
The Friends of the Earth report says GM crops have "created novel and alarming environmental problems such as genetic contamination".
"Contrary to the promises made by the biotech corporations the reality of the last 10 years shows that the safety of GM crops cannot be ensured, that they are neither cheaper nor higher quality and that they are not the magical solution to solve world hunger," said Friends of the Earth spokesman Juan Lopez.
Genetic modification can involve the introduction of genes from one plant to another or switching genes between plants and animals to change the way they develop, usually to protect them from disease or enhance their commercial value.