The former vice president said that Mr. Trump's comments while speaking at the Trump National Golf Club in Bedminster, New Jersey, on Tuesday were "unwise", but he expressed confidence in Defense Secretary James Mattis and National Security Adviser H.R. McMaster.
Yang said that before joining the WTO in 2002, Taiwan had been subjected to the Section 301 investigations because its trade regulations had not been aligned with global norms.
On Saturday, administration officials said the new trade measure was "totally unrelated" to events involving North Korea.
"This is simply not fair", said the official who spoke on condition of anonymity.
As the crisis has unfolded, Trump has alternated praising China for its help and chiding it for not ratcheting up pressure on its Asian neighbour.
"I think China can do a lot more", Trump told reporters on Thursday.
The investigation, which one United States official said could take as long as a year, may prove to be a source of leverage to push China to do more to help contain a rising security threat from North Korea, which counts Beijing as its only powerful ally.
North Korea has lashed back at the USA following President Donald Trump's latest warnings.
China Central Television on Saturday cited Xi as saying that Beijing and Washington are both interested in the denuclearization of the peninsula.
"At present, relevant parties should exercise restraint and avoid words and actions that would escalate tensions on the Korean Peninsula", Xi said, according to the statement provided by China's government.
The Chinese Ministry of Commerce has stressed the importance of China-US trade ties and urged the US authorities to abide by WTO rules in its trade measures. China is the North's biggest economic partner and source of aid, but says it alone can't compel Pyongyang to end its nuclear and missile programs. This past week, Trump said he could soften his views on trade if China stepped up its assistance, leading to speculation that the investigation could be a negotiating tactic.
They said that U.S. companies had long suffered because of Chinese intellectual-property violations, and that they expected Congress and the business community to support the measure.
"China's unfair trade practices and industrial policies, including forced technology transfer and intellectual property theft, harm the U.S. economy and workers", a second official said.
Trump has requested similar inquiries on trade, but the reports haven't been delivered on deadline.
Similarly, the president also asked for a review about whether steel and aluminium imports were jeopardizing national security.