US President Donald Trump took a pessimistic view of talks with European Commission President Jean-Claude Juncker set for Wednesday aimed at averting a trade war.

In a tweet on Tuesday night, Trump said both the United States and the European Union should drop all tariffs, barriers and subsidies.

"That would finally be called Free Market and Fair Trade!" Trump said. "Hope they do it, we are ready - but they won't!" he said.

Trump has accused the EU of unfair trade practices and has threatened to raise tariffs on cars imported from the bloc.

European Trade Commissioner Cecilia Malmstrom, who will accompany Juncker, said last week that the EU was preparing a list of US products to hit if the United States imposed the tariffs.