The final round of talks began at 0900 GMT on Wednesday with delegates deciding to "postpone" the adoption of an agreement to protect biodiversity.

The talks could not resolve disagreements between countries which produce genetically altered foods and the rest of the world.

Their aim had been a legally-binding protocol on reducing the risks of cross-border movement of GM organisms.

The meeting, in the city of Cartagena, involved delegates from the countries which have signed the UN Convention on Biological Diversity.

US accused

The United States had been accused of trying to wreck the talks. It has not ratified the convention but was in Cartagena as an observer.

But it has used that restricted status to orchestrate a refusal to allow the meeting to include commodities like soya beans and corn in the negotiations. The two crops make up 90% of the world trade in GM organisms.

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If the commodities were included, it would mean labelling them in international trade. That could mean they were boycotted.

The failure to reach agreement means there is no global agreement that a country has the right to refuse to allow the import of GM organisms. If individual states do refuse, they will be liable to challenge at the World Trade Organisation.

Greenpeace accuses the Americans of threatening biodiversity in the name of profit.

Greenpeace's political adviser, Louise Gale, said: "The US has attempted to terminate the Biosafety Protocol".

"It seems that the US, driven by the commercial interests of companies such as Monsanto, is willing to threaten the world's biodiversity and forego any international safeguards on the trade in GMOs."

Britain criticised

The US observers did have the support of five delegations, most of them from major grain exporting countries - Canada, Argentina, Australia, Chile and Uruguay.

The British delegation is also accused of giving support to the Americans after it helped to draw up a set of proposals which favour their position.

Dr Doug Parr, of Greenpeace UK, said that failed talks would mean that millions more consumers would be denied a choice about what they eat and a majority of the world's national governments would be powerless to enforce this basic individual right.

He also criticised the UK Government's policy on GMOs.