This maize strain entered EU markets as seed, food and animal feed. How, when and where remain unknown, officials say.

"(European Food Safety) Commissioner Markos Kyprianou deplores the fact that a GMO which has not been authorised through the EU's comprehensive legislative framework ... has been imported into the European Union," Commission spokesman Philip Tod told a daily news briefing.

Up to eight kilograms (17.6 lb) of Bt-10 seeds, within a 100-kg lot of Bt-11 seeds, were sent from the United States into France for research during this time, not for commercial growing. Two kg went to Spain. All the seeds have since been destroyed.

"In addition, we are told that an estimated 1,000 tonnes of Bt-10 food and feed products may have entered the EU through the Bt-11 export channel since 2001," Tod said.

EU authorities had demanded a full scientific risk assessment from Syngenta for Bt-10 and an official view from the US government on quantities exported to EU countries, he said.

Imports of Bt-11 maize were approved by the EU for use in industrial processing in 1998. The product is mainly used in animal feed rather than in food production.

But Bt-10 maize contains a gene making it resistant to an important group of antibiotics, which Bt-11 does not have. All GMO feed and foods made from GMOs, whether GMO material exists in the final product or not, must be labelled in the EU.

But there is one major loophole: there is no requirement to label products such as meat, milk or eggs obtained from animals fed with GMO feed or treated with GMO medicinal products.

Green groups are furious at the idea of an unapproved GMO finding its way into Europe, saying the Commission should have demanded information sooner to bring the problem under control.