Beijing has hit out at the U.S.' decision to impose sanctions on Chinese painkiller manufacturers. 

"I must point out that China already added all kinds of fentanyl-related substances to our control list, but the U.S. continues to this day not take lasting measures," Chinese Foreign Ministry spokesman Wang Wenbin said at a regular press conference on Wednesday.

Washington is trying to curb an addiction epidemic that killed a record 100,000 Americans last year. The U.S. claims China remains a major source of synthetic drugs. But Beijing says it has taken measures.