In the wake of the worst financial crisis since the Great Depression, EU governments and the Obama administration see a deep and broad free-trade deal as the best way to create jobs, removing burdens and customs duties on businesses.
But eight months into the talks, public hostility has grown toward the idea of unfettered trans-Atlantic commerce, while negotiators remain far apart on many issues.
Reports of the scale of U.S. National Security Agency spying in Europe have combined with concerns about the potential damage to food safety and the environment under a free-trade pact.
Obama said he had campaigned all his career for consumer rights and environmental protection and would not be party to an agreement that lowered standards. Protesters were reacting to distorted rumors around the trade talks, he said.
In both the United States and Europe, unions worry about job losses or reductions in working standards, and say a trade pact will serve the interests only of multinational companies.
Obama began his visit to Belgium by visiting the Flanders Field American war cemetery, visiting the graves of some of the 368 U.S. service members, most killed during World War I.
His visit and the symbolism of trans-Atlantic unity had added resonance at a time when tensions in Europe are running high because of Russia's military occupation and annexation of Ukraine's Crimea region.
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"This hallowed ground reminds us that we must never, ever take our progress for granted. We must commit perennially to peace, which binds us across oceans," Obama said.
If there were any doubts about the EU-U.S. relationship after last year's revelations of the scale of Washington's spying on its allies, Obama planned to assuage them later in the day, in a speech to some 2,000 guests, before leaving for Rome.
National Security Agency eavesdropping on Europeans' emails and mobile phones was mentioned only briefly at the joint news conference, with Van Rompuy welcoming Obama's initiatives to curb excesses by U.S. intelligence services and to reach a balanced data protection agreement with the EU by this summer.
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