BEIJING, Aug. 2 (Xinhua) -- A Chinese Foreign Ministry spokesperson said here Friday that the root cause of the fentanyl issue in the United States does not lie with China, urging the country to look harder for the cause at home.

"China always honors its pledges," said Foreign Ministry spokesperson Hua Chunying after a daily press briefing when asked to comment on U.S. President Donald Trump's post on Twitter on Thursday accusing Beijing of failing to fulfil promises to stop sales of the synthetic opioid fentanyl to the United States.

Hua said the Chinese government issued an announcement and offered detailed information on the class scheduling of fentanyl-related substances in April.

Relevant measures took effect on May 1, winning the acclaim of American people from all walks of life, she said.

The class scheduling of fentanyl-related substances is an important move by the Chinese government to ward off the risk and potential harm of new-type drugs to guarantee people's well-being and to participate in global drug control to safeguard security and stability of the world, Hua said.

"The root cause of the fentanyl issue in the United States does not lie with China. To solve the problem, the United States should look harder for the cause at home," Hua said.