MEXICO CITY (Reuters) - The United States and Mexico pledged to step up efforts to beat the growing threat of fentanyl, a synthetic opiate up to 50 times more lethal than heroin blamed for the deaths of thousands of people in recent years, including rock star Prince.

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A U.N. body in March added to an international list of controlled substances two chemicals used to make fentanyl, which the United States said would help fight a wave of deaths by overdose of the painkiller.

The Federal Commission for the Protection against Sanitary Risk “is finalizing revisions to the laws that will add these precursors to the list of controlled substances in Mexico. We encourage the rapid approval of these reviews,” U.S. Ambassador to Mexico Roberta Jacobson said in Mexico City on Tuesday as a two-day conference on fentanyl kicked off.

Over 33,000 people died in the United States in 2015 from opioid-related overdoses, including heroin or fentanyl, a 72 percent jump from a year earlier, Jacobson said. Among last year’s victims was music superstar Prince, coroners said.

“Current trends indicate that this figure will rise in 2016 and 2017,” Jacobson said, underscoring that halting the trade in opioids and other illicit drugs is “a No.1 priority for my government.”

During the conference, U.S. and Mexican law enforcement and regulatory agencies will share best practices for the detection, identification, analysis and management of fentanyl with Mexican forensic scientists.

The scientists are also being trained on the protocols for handling and storing fentanyl, as ingesting or absorbing even small amounts through the skin can be lethal, experts say.

Alberto Elias Beltran, a Mexican deputy attorney general responsible for international affairs, said tackling the problem would require better knowledge on consumption habits, seizures, modes of concealment, and manufacturing and distribution.

“In Mexico, so far in 2017 we have executed four seizures of this substance in different forms,” said Elias.

The head of counter-narcotics at the U.S. State Department, William Brownfield, estimated earlier this year more than 90 percent of the heroin currently consumed in the United States comes from Mexico, along with most of the fentanyl.

Brownfield said fentanyl was being trafficked by the same organizations moving heroin and other opioids from Mexico into the United States, but emphasized that most of the fentanyl entering the United States originated in China.