U.S. President Donald Trump on Monday stateside warned of steeper tariffs on China if exports of rare-earth magnets were curbed, threatening a precarious trade truce between the world's two largest economies.

"They have to give us magnets, if they don't give us magnets, then we have to charge them 200% tariffs or something," Trump told reporters after a meeting with South Korean President Lee Jae Myung at the White House on Monday.

Trump also said that airplane parts were a key leverage that Washington has to counter Beijing's grip on rare earths: "200 of their planes were unable to fly because we were not giving them Boeing parts purposely because they weren't giving us magnets."

Boeing has been working toward a deal to sell as many as 500 aircraft to China, with both sides fi

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