President Donald Trump has justified tariffs on Canadian imports by citing a flood of smuggled fentanyl. But nearly all of the powerful opioid is smuggled from Mexico.

Canadian and Chinese officials say they were already helping reduce fentanyl smuggling. Prime Minister Justin Trudeau said fentanyl crossing the northern border is "near zero."

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.

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.

China is willing to do more to address U.S. concerns about illicit fentanyl trade, an official from the Ministry of Foreign Affairs told reporters Wednesday.