U.S. tightens controls on China imports of nuclear components

Last month, U.S. President Donald Trump imposed tariffs on nearly $200 billion of Chinese imports and then threatened more levies if China retaliated.China then hit back with tariffs on about $60 billion of U.S. imports.Washington announced the nuclear technology controls a day after the U.S. Justice Department said it had arrested and indicted a spy for China's Ministry of State Security on charges of economic espionage.