The talks come at a time of growing friction over snooping by the US National Security Agency on its allies.

France has demanded protection for its film and television industry.

The Washington talks are aimed at removing trade and investment barriers between the United States and the EU.

German Chancellor Angela Merkel said on Thursday that the talks remained the "highest priority".

Non-tariff barriers

Direct tariffs on goods and services between the two are already low, but there are other barriers such as regulatory and safety standards, inspection procedures, and preferences for domestic business.

Removing these could significantly reduce the costs for companies doing transatlantic business.

For example, European negotiators will be pushing for US states, cities and federal departments to drop preferences for American contractors.

In turn, Washington will be looking for the EU to open up its market to US biotechnology firms wanting to sell products like genetically-modified foods, something which remains controversial in Europe.

'Not easy'

"These negotiations will not always be easy but I am sure they will be worth it," Jose Manuel Barroso, the head of the European Commission, said at the Group of Eight conference last month, when the two sides officially agreed to open talks.

Last year, trade in goods between the United States and the EU was worth some 500bn euros ($650bn), with another 280bn euros ($359bn) in services and trillions in investment flows.

Trade talks wish list

Businesses on both sides of the Atlantic are eager for a free trade deal. Here's a selection of what's being negotiated:

• Brake lights: car manufacturers from Ford to BMW want standardised safety regulations, so they no longer have to manufacture separate parts to adhere to different safety standards
• Couriers: FedEx wants to modify rules restricting its use of trucks in historic sections of cities
• Champagne: currently, US winemakers in existence before 2006 can mark their bubbly with the word "champagne." They want to keep that rule in place
• Wal-Mart: the world's largest retailer wants to prevent regulations on online shopping
• Chicken: Campbell Soup and US poultry producers want to scrap an EU rule banning US chickens treated with chemicals