From next week, US exports to Europe of corn gluten feed and brewers grains, a by-product of ethanol, must be certified by an internationally-accredited laboratory to show there is no presence of Bt-10 maize, a GMO that is not authorised in Europe.

These measures will be reviewed at the end of October. US exporters send 3.5 million tonnes of corn gluten feed to Europe each year, a trade worth some 350 million euros ($449 million).

"Imports of maize products which are certified as free of Bt-10 will be able to continue, but at the same time we cannot and will not allow a GMO which has not gone through our rigorous authorisation procedures to enter the EU market," EU Health and Consumer Protection Commissioner Markos Kyprianou said.

Last month Swiss agrochemicals group Syngenta said some of its maize seeds sent to the EU from the United States were mistakenly mixed with Bt-10. This insect-resistant strain is similar to Bt-11, a different GMO strain that won EU approval for distribution in 1998.

Syngenta said it respected the Commission's decision "to ensure compliance with the existing regulations".

"We are fully committed to continue co-operation with all concerned parties," Mike Mack, chief operating officer of Syngenta Seeds, said in a statement.

OVER-REACTION, SAYS US

In Europe, consumers have been far more reluctant than in the US to accept GMO products, often dubbed as "Frankenstein foods", while manufacturers of GMO foods insist they are safe.

US officials condemned the EU move.

"We view the EU's decision to impose a certification requirement on US corn gluten due to the possible, low-level presence of Bt-10 corn to be an over-reaction," said Edward Kemp, spokesman at the US mission to the European Union.

"US regulatory authorities have determined there are no hazards to health, safety or the environment related to Bt-10," he said. "There is no reason to expect any negative impact from the small amounts of Bt-10 corn that may have entered the EU."

The maize mix-up occurred sometime between 2001 and 2004.

Small amounts of seeds, up to 10 kilograms, arrived in France and Spain from US suppliers for research purposes. All the seeds have since been destroyed.

Some 1,000 tonnes of Bt-10 maize also entered the EU as food and animal feed but it is still not clear to which countries. Around 70 percent of this is thought to be animal feed.

Green groups said the decison amounted to an effective ban on imports of US maize-based feeds for the foreseeable future.