U.S. President Donald Trump warned on Monday that Washington could impose tariffs of up to 200 percent on China if it refuses to export magnets to the United States.

Speaking at the White House during a joint press event with South Korean President Lee Jae-myung, Trump said U.S.-China economic relations are now “much better” than before, adding that Beijing is “acting wisely” but has effectively monopolized the global magnet market.

“They have to supply us with magnets, and if they don’t, we’ll have to impose tariffs of 200 percent or something like that,” Trump told reporters.

The warning follows Trump’s April 2 announcement of additional tariffs on several U.S. trade partners, including China, as part of his administration’s broader trade policy.