The European Union could hit the United States with counter-tariffs on 93 billion euros ($109 billion) worth of U.S. goods if the two sides fail to reach a trade deal by Washington's August 1 deadline for imposing import levies.

Combining goods, services and investment, the EU and the United States are each other's largest trading partners by far. The American Chamber of Commerce to the EU warned in March that any conflict jeopardised $9.5 trillion of business in the world's most important commercial relationship.

The EU says its negotiators are working "might and main" on a deal, but the decision rests with US President Trump.