Support is growing in the US to escalate a dispute with Brussels over genetically modified food, further straining transatlantic relations over trade policy.

US Trade Representative Robert Zoellick said he supported calls for action against the European Union over its moratorium on genetically modified food products.

"I personally am now of the view that we need to bring a case," Mr Zoellick said, urging that the EU be brought before the World Trade Organisation.

And he said that his position was winning support in Washington.

"My sense was that there is pretty broad agreement on this but I don't want to presume everybody else's position."

While stating that a final position would need Cabinet approval, he urged action "sooner rather than later".

Fight back

The statement will strain Washington-Brussels trade relations already strained over levies on US steel imports, and agriculture subsidies.

EU Trade Commissioner Pascal Lamy said Europe would fight any attempt by the US to force it to open its markets to genetically modified crops.

"If there was to be litigation, of course we would fight it and I believe we would win it," he said.

A complaint to the WTO would only make finding a solution "more complex, rather than more simple", Mr Lamy added.

Controversial technology

The US has proved a champion of genetically modified crops, which include extra genes added to bring characteristics such as pest resistance, or improved vitamin content.

GM supporters believe the crops could be a major ally in the war against famine in developing nations.

"I find it immoral that people are not being able to be supplied food to live in Africa because people have invented dangers about biotechnology," Mr Zoellick said.

But the technology has also sparked considerable concerns over potential side effects, and the possibility of genes being transferred from GM crops to wild plants.

The EU has for four years refused to approve products such as foods and pharmaceuticals including ingredients derived from genetically-modified crops.

While Mr Zoellick last February threatened to take the EU to the WTO, the dispute over the issue had appeared, last autumn, to have subsided.