Bags of heroin, some laced with fentanyl, are displayed before a press conference regarding a major drug bust, at the office of the New York Attorney General, September 23, 2016 in New York City.

Washington welcomed China's move on Monday to expand the range of fentanyl-related substances it defines as controlled narcotics, after criticism from President Donald Trump for allowing the synthetic opioid to be shipped to the United States.

The United States is battling an epidemic of opioid-related deaths, and U.S. Trade Representative Robert Lighthizer has said he hopes to include China's commitments to curb the drug in any agreement to end the two countries' bitter trade war.

"This significant development will eliminate Chinese drug traffickers' ability to alter fentanyl compounds to get around the law," the U.S. Drug Enforcement Agency said in a statement.

"We look forward to our continued collaboration with China to reduce the amount of this deadly poison coming into our country," the DEA statement said.

Earlier on Monday, China had announced the expanded control of fentanyl-related substances at a press conference, even as it blamed U.S. culture for abuse of the drug.

China said the addition of fentanyl-related substances to the supplementary list of controlled narcotic drugs will take effect on May 1. Fentanyl itself and its "analogues" had previously been listed and remain controlled.

"Resolved. All resolved," Liu Yuejin, a senior public security ministry official and vice commissioner of the China National Narcotics Control Commission, told reporters when asked if U.S. concerns had been resolved.