BEIJING — China’s newly appointed economic czar told Treasury Secretary Steven Mnuchin on Saturday that Beijing was ready to defend its interests after President Trump announced plans to slap tariffs on billions of dollars’ worth of Chinese imports.

Vice Premier Liu He told Mr. Mnuchin in a phone call that the order Mr. Trump signed on Thursday violated international trade rules, China’s official Xinhua News Agency reported.

The White House says the planned tariffs are intended to punish Beijing for what it depicts as the theft of American technology.

Xinhua quoted Mr. Liu as saying that China was “ready and capable of defending its national interest and hopes both sides will remain rational.”