United States President Donald Trump said on Wednesday the United States might have to "unwind" trade deals it reached with the European Union, Japan and South Korea, among others, if it loses a Supreme Court tariffs case, and warned that a loss would cause the U.S. "to suffer so greatly."

Trump, speaking to reporters at the White House, said his administration will ask the Supreme Court to reverse a U.S. appeals court ruling last week that found many of his tariffs were illegal. Trump, however, said he thought his administration would prevail in the case.

Trump said rescinding the tariffs would be costly, although trade experts note that the duties are paid by importers in the U.S., not companies in the countries of origin. Economists have warned that tariffs are likely to fuel inflation in the U.S.

The appeals court ruling addressed the legality of what Trump calls "reciprocal" tariffs first imposed as part of a trade war in April, as well as a separate set of tariffs imposed in February against China, Canada and Mexico. The decision does not impact tariffs issued under other legal authority, such as those on steel and aluminum imports.

Ryan Majerus, a former senior U.S. trade official, said it had been clear from the start that the trade deals with the EU and other trading partners were framework agreements that were subject to change, not fully fledged trade agreements.

U.S. Senator Ron Wyden, the top Democrat on the Senate Finance Committee, said Trump's comments sowed more confusion.

(With input from Reuters)