Hi, this is Colum Murphy in Beijing, where Chinese officials are throwing a few sharp elbows in their running rivalry with the US.

China said on Wednesday that the U.S. has undermined bilateral counter-narcotics cooperation by imposing tariffs on Chinese goods over fentanyl, calling on Washington to stop using the issue as a bargaining chip to "blackmail" the country.

Trump cited the fentanyl issue as the reason for imposing a 10% tariff on all Chinese imports in early February, on top of any existing duties. He doubled that to 20% earlier this month. He also has cited fentanyl, along with other reasons, for imposing tariffs on Canada and Mexico.