The European Commission announced Thursday that it has decided to impose mandatory tests on all imports of US long grain rice, after a banned genetically modified strain entered the European market.

The Commission said in a statement that it wanted to impose the "counter testing", for which exporters will foot the bill, because it had failed to agree with US authorities on a common testing and sampling regime.

"Despite extensive discussions between both sides, the commission and the USA were unable to agree on such a protocol," the statement said.

The move comes after two consignments of US rice brought into Belgium and the Netherlands early last month and certified GM-free were found to be contaminated with the banned genetically modified LLRICE601 strain.

They were part of a cargo of 20,000 tonnes of US rice suspected of being contaminated with LLRICE601 which was blocked at Rotterdam port last month.

Three of the 23 lots of rice tested were positive for the unauthorised strain but the bulk of the consignment was allowed on to the European market.

France, Sweden and Germany had also discovered traces of the banned rice, but it did not come from the Rotterdam source.

The European Food Safety Agency has said that the contaminated rice "is not likely to pose an imminent safety concern to humans or animals".

LLRICE601 was created by Bayer Crop Science, a German-based multinational with a range of gene-altered crops. It was an experimental variety that the company stopped working on five years ago and did not intend to sell.