US President Donald Trump has said the United States and the European Union have agreed to work on lowering trade barriers as they seek to head off a brewing trade war.

He was speaking after a meeting with European Commission President Jean-Claude Juncker at the White House.

"This was a very big day for free and fair trade, a very big day indeed," President Trump told reporters.

"We are starting the negotiation right now but we know very much where it's going," he said.

Speaking with Mr Juncker at his side, President Trump said they had agreed in talks to "work together toward zero tariffs, zero non-tariff barriers, and zero subsidies on non-auto industrial goods."

"We will also work to reduce barriers and increase trade in services, chemicals, pharmaceuticals, medical products, as well as soybeans; soybeans is a big deal," he said, adding that Europe would also step up purchases of liquefied natural gas from the US.

Mr Trump said the talks would "resolve" both the hefty tariffs the US has placed on imports of steel and aluminium from the EU and the tariffs Europe had slapped on US goods in response.

It is not clear whether the two sides made any progress on the contentious issue of possible US tariffs on imports of automobiles from Europe.

But Mr Juncker said they had agreed not to impose any new tariffs while talks were taking place.

"This was a good and constructive meeting," he said.

President Trump has threatened to impose 25% tariffs on auto imports, a move that would hit European carmakers like BMW and Volkswagen hard, as well as Japanese and South Korean car companies.

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