"The biggest challenge China faces in cracking down on the smuggling of opioids is the huge demand from the US," said Yu Haibin, a senior official with the Narcotics Control Bureau of the Ministry of Public Security, the country's top law enforcement agency.
"The United States should strengthen its educational and publicity campaigns to reduce domestic demand, intensify its crackdown on internet-based drug crimes, and share more lab data with China to improve our detection and verification capabilities."
Yu also took a jab at America's changing drug environment and its impact.
"Quite a number of US states have legalized medical or even recreational use of marijuana," he said at a press conference Thursday. "I think this trend has had a negative effect on public recognition or mentality on the opioid problem."
US President Donald Trump in October declared the opioid crisis a public health emergency. A report from the Congressional US-China Economic and Security Review Commission last February labeled China as the primary source of fentanyl -- a cheap synthetic opioid at least 50 times stronger than heroin -- in the US, citing law enforcement and drug investigators.
During his state visit to China last month, Trump brought up the topic with his Chinese counterpart Xi Jinping in Beijing. The two leaders agreed to bolster mutual cooperation on fighting narcotic crimes -- and the Chinese authorities on Thursday emphasized recent progress despite some choice words for Washington.
After announcing the listing of five new chemicals -- used to make fentanyl or methamphetamine -- as controlled substances, Chinese officials highlighted their latest success in destroying a fentanyl lab in northern China thanks to a tip from the US immigration and customs agency.
The joint China-US effort resulted in the arrests of 19 suspects in recent months across China as well as the seizure of 4.7 kilograms (10 pounds) of fentanyl and more than 150 kilograms of drug ingredients, according to Chinese officials.
Addressing rising concerns over online sales of opioids originated from China, Yu said the government has stepped up "internet patrol" as well as mandated real-name registration and inspection for all outbound international packages.
Echoing other Chinese officials, though, Yu again cited "insufficient evidence" to push back at the claim that China is the main source of cheap and deadly synthetic opioids flooding into the United States.
He also confirmed the lack of development in the case of two Chinese nationals indicted by the US Justice Department in October for manufacturing and distributing large quantity of fentanyl and other opiates in the US, calling it an "open case still under investigation."
Public health crisis
Since 1999, the number of American overdose deaths involving opioids has quadrupled. From 2000 to 2015, more than half a million people died of drug overdoses, and opioids account for the majority of those. Recently released numbers from the US Centers for Disease Control and Prevention found that around 64,000 people died from drug overdoses in 2016.
Representatives from the US embassy -- as well as diplomats from Europe and Asia Pacific -- attended Thursday's press conference but did not speak.
In a similar event last month, a US official stressed cooperation between the two countries in Washington's war on opioid abuse.
"Once China controls the substances, it has dramatic effects in the United States in terms of lives saved," said Lance Ho, the US Drug Enforcement Administration's country attaché in Beijing. "Once they do that, we see a decrease in the usage in the United States."