The United States and European Union aim to start negotiating a vast Transatlantic free trade pact by June, though the plan confirmed on Wednesday faces many hurdles before it might help revive the world's top two economies.

A deal would be the most ambitious since the founding of the World Trade Organization (WTO) in 1995, embracing half of world output and a third of all trade. It reflects impatience with the lack of a new global agreement to cut tariffs and ease commerce.

But after a year of preparatory discussions between Brussels and Washington, major differences remain, such as EU resistance to importing U.S. foodstuffs that are genetically modified.