US Secretary of State Antony Blinken on Friday urged the international community to fight together against synthetic drugs including the powerful opioid fentanyl, which has killed tens of thousands of Americans.

"My message to this gathering is urgent. If we want to change the trajectory of this crisis there is only one way to succeed -- together," Blinken told delegates at a conference of the United Nations Office on Drugs and Crime (UNODC).

"This is, simply put, a problem that no one country can solve alone," he said.

The United States has been ravaged by fentanyl abuse in recent years, with tens of thousands of deaths attributed to the drug annually.

The synthetic opioid 50 times more powerful than heroin and much easier and cheaper to produce.

US President Joe Biden, campaigning for his re-election in November, has made the crisis a priority.

Blinken said the US was looking to earmark $175 million for the next fiscal year for a global fight against synthetic drugs.

UNODC executive director Ghada Waly told the gathering that synthetic drugs were compounding the threat of traditional, plant-based illicit drugs.

"Synthetic drugs have changed the landscape, making it cheaper and easier to produce and smuggle extremely potent and often lethal substances," she said in her opening remarks for the conference on Thursday.

"Drugs such as fentanyl are causing record overdose deaths, while clandestine production labs are sprouting up in new parts of the world," she added.

The US set up a coalition to combat synthetic drug threats last year that now includes 149 countries.

Washington has notably been putting pressure on China, one of the primary sources of fentanyl production, along with Mexico.

In early February, a US delegation met with Beijing officials to discuss the issue.

No bilateral meeting between US and Chinese officials is planned in Vienna, according to an American diplomatic source.

Beijing has dispatched Andy Tsang Wai-hung, deputy director of its National Narcotics Control Commission, to the conference, while Russia is represented by deputy foreign minister Sergey Vershinin.

Fentanyl is responsible for more than 70,000 overdose deaths in the United States each year, making it the leading cause of death of people aged 18 to 49, officials have said.