US President George Bush has accused Europe of blocking efforts to fight famine in Africa because of "unfounded" fears over genetically modified foods.
Scientific opinion is divided over GM crops
He accused European nations of "impeding" US efforts to reduce hunger in Africa by opposing the use of GM crops.
The US plans to sue the European Union at the World Trade Organisation unless it allows the sale of GM foods and crops.
US seed companies are keen to sell their products to foreign markets, but European consumers are wary of GM foods, fearing long-term harm to human health and the environment.
Our partners in Europe have blocked all new bio-crops because of unfounded, unscientific fear
Mr Bush, who is visiting Europe in early June for a G8 summit, said GM foods could help end hunger in Africa.
"Our partners in Europe have blocked all new bio-crops because of unfounded, unscientific fears," he said in a speech on Wednesday.
"This has caused many African nations to avoid investing in bio-technologies for fear that their products will be shut out of European markets."
Zambia says no
GM food aid was sent to southern Africa during the current drought, despite strong reservations from Africa.
Zambia banned the aid, saying it would rather go hungry than risk losing its export markets in Europe because its crops had been contaminated with GM seed.
The BBC's Martin Plaut says the Bush administration has taken a more commercial approach than Europe towards Africa.
He says the US makes great play of the fact that it has helped African states get an official credit rating, which they need to raise bank loans.
Europe's approach has traditionally been to provide direct funding for projects like roads or dams.
The GM debate is expected to come up when President Bush visits France next weekend.
Correspondents say the EU is likely to resist calls for it to lift its block on GM food imports. It is also developing tough new labelling regulations which worry US farmers.