The head of the U.N. drug watchdog agency is urging U.S. federal officials to challenge the decriminalization of possessing small amounts of marijuana for adults 21 and over in Washington and Colorado.
While marijuana remains illegal under federal law, both states legalized possession of up to an ounce in November and are setting up rules to govern growers, processors and retailers.
Raymond Yans of the Vienna-based International Narcotics Control Board said in a statement Thursday that Washington is obliged to ensure nationwide implementation of a drug convention "to which the United States is party" and which bans recreational marijuana use.
The INCB has no enforcement ability.
U.S. Attorney General Eric Holder said last week the Justice Department has not yet decided whether to sue to block the measures.