The European Union Commission is preparing to introduce tariffs on $20 billion of US goods if Washington imposes trade levies on imported cars, EU trade commissioner Cecilia Malmstrom told the Swedish newspaper Dagens Nyheter on Wednesday.

"We hope that it doesn't come to that and that we can a solution. If not, the EU Commission is preparing a rather long list of many American goods. It would be around $20 billion," she said.

Any new European tariffs will not be directed at specific American states, she said. "No, now it's more general goods such as agricultural products, machinery, high-tech products and other things," she said.

She said that she didn't think US Treasury Secretary Steven Mnuchin's proposal to drop tariffs, non-tariff trade barriers and subsidies was serious, pointing out that the US has laws and subsidies protecting American industries.

"We tried earlier in TTIP negotiations to make the United States loosen those laws. It was completely impossible. They did not move a millimeter," Malmstrom told Dagens Nyheter.

Malmstrom is part of EU delegation in Washington for talks on Wednesday on a long-term trade deal.

"Basically, I'm an optimistic person, but heading in to this I'm moderately optimistic. But one must always try."