Pence, who has often struck a hawkish tone on China, spoke just weeks before Trump is due to attend a summit in Chile where he has said he hopes to close a "phase one" trade deal with Chinese President Xi Jinping.

Another flashpoint has been a widening controversy over a tweet from a U.S. National Basketball Association official. His backing of Hong Kong democracy protests was rebuked by the NBA, sparking a backlash.

The Chinese Basketball Association said Sunday on its official Twitter-like Weibo account that Daryl Morey had made "improper remarks regarding Hong Kong'' to which it expressed its "strong opposition.''