"Exports of corn gluten feed from the US which are accompanied by this analytical report would be allowed to enter the EU, but without this analytical report they would not be allowed to enter the EU," the source said on Tuesday.

The European Commission, the EU's executive arm, has asked Syngenta to provide a detection method for Bt-10, which got mixed up with another, authorised biotech maize called Bt-11. Syngenta has not yet done so.

The mix-up occurred between 2001 and 2004.

The EU and European consumers have been far more reluctant than the United States to embrace GMO products, which some European newspapers have labelled "Frankenstein foods". Creators of GMO foods contend they are safe.

The Commission has previously said it might consider imposing a temporary ban on GMO animal feed made from maize gluten originating in the United States.

The EU imports 3.5 million tonnes of this type of feed from the United States each year.

The source said EU member states made clear in a meeting on Tuesday that they found it unacceptable that the United States could not give any guarantees on the issue.

MEASURES TO BE ACCELERATED

EU Health and Consumer Protection Commissioner Markos Kyprianou has a mandate from the EU executive to come up with a proposal for the problem, the source said.

"We're talking about a measure which would say that exports of corn gluten feed essentially should be certified, should be accompanied by an analytical report by an accredited laboratory certifying that these exports are free of Bt-10," he said.

He said the measures would be accelerated through the EU decision-making procedures.

"We believe it is a matter of urgency and that the measures should be in place as soon as possible," the source said.

Up to eight kilos (17.6 lb) of Bt-10 seeds, within a 100-kg lot of Bt-11 seed, arrived in France for research between 2001 and 2004 from US suppliers, not for commercial growing. Two kg went to Spain. 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 not clear to which countries. Around 70 percent of this is thought to be animal feed. EU authorities still do not know how, when and where all this happened.

Environmental group Greenpeace called on the EU in a statement to impose a ban on "all food and feed crops and seeds from the US as long as EU authorities do not have the means to test imports for illegal genetically modified organisms."