As President Trump visits China next week, his vow to press for more stringent drug controls may run into resistance from a government loath to accept full responsibility for its role in the United States’ opioid problem.

In declaring opioids a public health emergency last week, Mr. Trump said that he would raise the issue of “the flood of cheap and deadly fentanyl” made in China as a top priority in his meeting with President Xi Jinping on Wednesday.

But on Friday, a Chinese official, Wei Xiaojun, disputed the assertion that China was largely to blame.

“Based on the intelligence and evidence shared” between the countries, there is no reason to conclude that “a large portion” of the fentanyl and similar substances in America comes from China, said Mr. Wei, deputy director of the narcotics control bureau at the Ministry of Public Security.