Mr. Trump has pointed to China as the drug’s main source, saying it is “either shipped into the United States or smuggled across the southern border by drug traffickers.” Last year in the United States, about 64,000 people died of drug overdoses.
A congressional commission in the United States has also found fault with China.
“China is the main supplier of fentanyl to the United States, Mexico, and Canada,” the U.S.-China Economic and Security Review Commission said in a report in February, citing law enforcement and drug investigators.
The Chinese authorities “place little emphasis on controlling its production and export,” according to the report.
Analysts say the country’s poorly regulated chemicals industry has helped fuel a booming trade in fentanyl.
Under pressure from the United States, Beijing has banned the manufacture and sale of 23 variations of the synthetic drug, including four types this year, which a spokesman for the American Drug Enforcement Administration called a “potential game-changer” in February.
China takes a strict stance on narcotics domestically, remembering how the country was ravaged by opium addiction in the 19th century, a factor in the Opium Wars. Chinese officials say that they are trying hard to combat fentanyl exporters but that doing so is a cat-and-mouse game, with drugmakers easily modifying their products to avoid detection.
Mr. Wei criticized the Department of Justice’s public announcement last month of indictments against two “major Chinese drug traffickers — a case that both Beijing and Washington were working on.”
Last week the department highlighted the indictments against Yan Xiaobing and Jian Zhang, who are living in China, as a sign that the United States was making its fight against opioids a global one.
Saying it would hinder the investigation, Mr. Wei said, “China regrets that the U.S. chose to unilaterally hold a news conference to announce the hunt for these fugitives.”
China has no extradition treaty with the United States, and Mr. Wei said a decision on extraditing the two men would be dependent on evidence that the Americans could provide or the Chinese could unearth.
Saying that fentanyl abuse does not exist in China, Mr. Wei said the authorities had nonetheless responded forcefully to the crisis in the United States by banning more fentanyl analogues than those on a United Nations drug body’s list of controlled substances.
He stressed that “the Chinese government takes into full account the concerns of the international community, including the United States, and has continued to take legislative measures and actions” to control the flow of illicit drugs.
“Once China controls a substance, it has a dramatic effect on the United States in terms of lives saved,” Lance Ho, the Beijing-based country attaché for the Drug Enforcement Administration, said at the news conference.