President Donald Trump plans to impose a duty of 25 percent on steel and 10 percent on aluminium to counter cheap imports, especially from China, that he says undermine US industry and jobs.

"Norway has not prepared retaliatory measures. I believe there should be a high threshold for taxing Norwegian consumers and businesses by imposing restrictions on trade," Soereide, of Norway's ruling Conservative Party, was quoted as saying.

Norway is not a member of the European Union, which plans to respond to the US measures with tariffs of its own.

State-controlled Norsk Hydro ASA is among the world's top makers of aluminium but most of the exports go to European countries.

Other Norwegian firms export a range of commodities, such as oil, natural gas, fish and fertilisers, and depend on a well-functioning international system of trade, Soereide said.