Senior officials from China and the United States have been “testing the waters” ahead of US President Donald Trump’s coming visit to China by outlining some of their main concerns.Meanwhile, new areas of concern emerged on Friday as the Chinese Ministry of Commerce warned that the United States was threatening the “hard-won stability” in their trade relations after the national telecoms agency effectively banned smartphones tested in Chinese laboratories from the American market.Chinese Foreign Minister Wang Yi also referred to “hard-won stability” a day earlier in a phone call with US Secretary of State Marco Rubio, with Wang describing Taiwan as “the biggest risk factor in China-US relations”.“The Taiwan issue concerns China’s core interests and is the biggest risk factor in China-US relations,” Wang said.“The US side should honour its commitments, make the right choice, open up new space for China-US cooperation and do its part to promote world peace.”Wang also said the two sides must “make thorough preparations for the coming high-level engagements”, according to state broadcaster CCTV.This appeared to refer to the possible meetings between Chinese President Xi Jinping and his US counterpart Donald Trump this year, including one that the White House said would take place in Beijing in the middle of this month.