VIENNA—The head of the U.N. drug watchdog agency is urging U.S. federal officials to challenge ballot measures in Colorado and Washington that decriminalized possession of small amounts of marijuana for adults 21 and over.

Raymond Yans says the approvals send “a wrong message to the rest of the nation and it sends a wrong message abroad.”

Yans heads the International Narcotics Control Board. He told The Associated Press on Tuesday he hopes Attorney General Eric Holder “will take all the necessary measures” to ensure that marijuana possession and use remains illegal throughout the U.S.

Both states are holding off on plans to regulate and tax the drug while waiting to see whether the Justice Department will assert federal authority over drug law.

The INCB has no enforcement ability.