U.S. President Donald Trump warned the European Union on Thursday of consequences that will be "severe economically" if Brussels fails to hold trade talks.

"The European Union treats us very, very unfairly," Trump told reporters at the White House.

"They're willing to talk to us. If they don't talk to us we'll do something that will be severe economically. We'll tariff a lot of their products coming in."

Amid rising trans-Atlantic tensions and fears of an all-out trade war, Trump and EU Commission President Jean-Claude Juncker agreed in July to start talks intended to achieve "zero tariffs" and "zero subsidies" on non-automotive industrial goods.

Trump imposed tariffs of 25 percent on steel imports and 10 percent on imported aluminum from the EU on June 1. He said the move was to protect U.S. national security interests, but the Europeans claim it is simply protectionism and breaks global trade rules.

The EU introduced "rebalancing" tariffs on about 2.8 billion euros worth ($3.4 billion) of U.S. steel, agricultural and other products.

Trump has held out the threat of slapping auto tariffs on European cars should the trade talks fail to progress.