A U.N.-based drug agency says the legalization of marijuana for recreational use in Colorado and Washington violates international drug treaties.

The International Narcotics Control Board is urging the Obama administration to challenge the legalization measures. It made the appeal in its annual drug report released Tuesday.

U.S. Attorney General Eric Holder said last week that he was in the last stages of reviewing the state laws. Holder said he was examining policy options and international implications of the issue. Marijuana is illegal under federal law.

The federal government could sue the states over legalization or decide not to mount a court challenge.

The control board is the independent monitoring body for the implementation of United Nations drug control conventions. Its head also called on Holder to challenge the laws in November.