Beijing (CNN) China's top drug control body has hit back at recent claims by US President Donald Trump that Chinese suppliers are fueling America's opioid crisis.

Yu Haibin, a senior official with China's National Narcotics Control Commission, said in a press briefing Wednesday that Trump's comments were "unacceptable" and "irresponsible."

Trump tweeted last week that it was "outrageous" that China-produced fentanyl, a cheap and deadly synthetic opioid at least 50 times stronger than heroin, continued to "pour into the US" through international mail.

Yu said the Chinese government found Trump's tweet "completely unacceptable."

"The United States has no proof that most fentanyl in the country comes from China," he said. "It's highly irresponsible to draw such a conclusion based on some individual cases."

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