After calling out China and Russia, he said even "people that we think are wonderful" -- the European Union -- have erected trade barriers that are "far worse than tariffs."

The EU has vowed to retaliate against US-made consumer goods such as Harley-Davidson motorcycles and blue jeans.

"We're not backing down," Trump said.

And if the ongoing renegotiation of the North American Free Trade Agreement with Mexico and Canada does not produce the desired result, Trump said he'll terminate the deal.

Still, he dismissed concerns about a trade war.

"I don't think you'll have a trade war," he said.

The proposed tariffs have met with rare opposition from members of Trump's own Republican Party, including House Speaker Paul Ryan of Wisconsin. Opponents argue that the new measures could erase economic gains from a recent corporate tax reduction.

Korea has been hesitant to act against the proposal as it is in the process of renegotiating its own free trade deal with the world's largest economy.

The Trump administration also imposed safeguard duties on Korean washers and solar panels earlier this year.(Yonhap)