BEIJING — China said Monday that it will tighten regulation of fentanyl-related substances as a gesture to the United States, where the synthetic opioid has caused tens of thousands of overdose deaths annually and fueled a public health crisis.

In a move first promised by Chinese leader Xi Jinping during a December meeting with President Trump, China will enact a blanket ban on variants of fentanyl-related substances.

For years, China’s vast chemical and pharmaceutical industry exploited loopholes in Chinese law to create synthetic painkillers and their precursors that were not explicitly banned.

U.S. officials including Trade Representative Robert E. Lighthizer have pushed Beijing to significantly broaden its list of scheduled substances to cover the entire class of synthetic opioids, their analogues and precursors, and crack down on their unchecked production and export.

China will expand the range of fentanyl-related substances it defines as controlled narcotics, but Beijing blames U.S. culture for abuse of the drug. (Reuters)

Liu Yuejin, a deputy commissioner at the China National Narcotics Control Commission, told reporters Monday that U.S. concerns about the unregulated production and export of opioids have been “resolved, all resolved.”

But Liu reiterated the long-standing Chinese government position that U.S. drug culture and overprescription by doctors — not China — were to blame for the widespread abuse of synthetic opioids, which can be 50 times more powerful than heroin and are now the leading source of overdose deaths in the United States.

Liu said China’s shipments of opioids to the United States were “extremely limited” — a claim that runs counter to allegations by U.S. law enforcement that the vast majority of fentanyl-like substances originate in China and enter the country through mail parcels.

“If the United States truly wants to resolve its fentanyl abuse problem, it needs to strengthen its domestic work,” Liu said. “Some people link drug consumption with freedom, individuality and liberation.”

U.S. officials generally say China has offered steady cooperation with Washington on fentanyl — a rare bright spot in bilateral relations — but some would like to see Beijing be more proactive.

A Washington Post investigation last month found that the Obama administration, at several junctures, did not grasp the role Chinese producers played in the fentanyl crisis or even the magnitude of the epidemic itself.

A 2015 review by a national interagency task force examining heroin and overdose deaths made no mention of China or how fentanyl is smuggled into the country by mail.

The broad opioid ban is part of a number of concessions China has offered as it seeks a trade deal, which could come in the weeks ahead. China in March fast-tracked a foreign investment law in a show of goodwill.

China’s Foreign Ministry said its top trade negotiator, Liu He, departed on Monday for Washington, where U.S. and Chinese negotiators are seeking to hammer out a deal that could be presented to Xi and Trump.

Negotiators met last week in Beijing for talks that yielded “new progress,” the Chinese government said.