WASHINGTON (Reuters) -President Donald Trump said on Wednesday the United States might have to "unwind" trade deals it has clinched with the European Union, Japan and South Korea, among others, if it loses a Supreme Court case on the legality of tariffs.

Trump, speaking to reporters at the start of a meeting with Polish President Karol Nawrocki, said his administration was asking the Supreme Court to reverse a U.S. appeals court ruling last week that found many of his tariffs were illegal.

Losing that case would leave the United States far poorer, and could jeopardize trade agreements made in recent months, he said, adding that he thought the administration would prevail.

"Our country has a chance to be unbelievably rich again. It could also be unbelievably poor again. If we don't win that case, our country is going to suffer so greatly, so greatly," he said.

Trump said his imposition of tariffs on most trading partners had paved the way for trade deals with the EU and others that were already completed, with others still being negotiated.

"We made a deal with the European Union where they're paying us almost a trillion dollars, and you know what? They're happy. It's done. These deals are all done," he said. "I guess we'd have to unwind them."

Trump's comments were his first suggesting that the trade deals reached with major trading partners could be invalidated if the Supreme Court lets Friday's ruling stand.