The ongoing dispute between the European Union and the US, over the EU's refusal to accept genetically modified food, has continued to escalate.
"No to GMO": French protestors make their feelings clear
The EU has criticised the US decision to launch a trade suit against its decision to keep GM crops out.
On Thursday the US requested the creation of a formal World Trade Organisation (WTO) dispute panel over the issue.
The request had been expected after the US and its partners in the dispute - Canada and Argentina - had failed to reach an agreement over the blocking of genetically modified crops.
But the EU insists its policy is valid.
"We very much regret this decision that's apparently been taken," said a spokeswoman for David Byrne, the EU health and consumer protection commissioner.
"We think our system of GMO (Genetically Modified Organisms) authorisation is clear, transparent and non-discriminatory, and complies with WTO rules."
The US and 12 other agricultural exporting nations are pushing the EU to end its five-year moratorium on GM crops.
They claim the motion is damaging developing countries and US farmers.
Biotech crops, including corn and soybeans that have been genetically modified to resist insects or disease, have been widely grown in the US for years.
"This trade barrier harms farmers and consumers around the world by denying them the benefits of productive, nutritious and environmentally friendly biotech products," said the US trade representative Robert Zoellick.
But the EU imposed the barrier because of concerns over food safety.
Last month, it agreed to two new GMO directives which it said would open the way to lifting the five-year moratorium.
In the first, it required that all foods and animal feed be labelled if they contain 0.9% GM ingredients or more.
WTO protests are already beginning
The second required that all GM foods' origins can be traced.
The US said the new rules would be too cumbersome to implement and made no difference to its case.
"For five years, the EU has kept in place its ban on biotech approvals, a ban which is unsupported even by the EU's own scientific studies," said Mr Zoellick.
The ongoing dispute is likely to occupy much of the debate at an international meeting of trade ministers in Mexico in September.
The talks follow stalled WTO negotiations, but some observers have suggested the row over GM crops will overshadow proceedings.
Another bone of contention between the EU and US are agricultural subsidies, expected to be another stumbling block.