MEXICO CITY, Mexico — The United Nations' drug law enforcement body has reprimanded Latin American countries that have decriminalized narcotic use, delivering a blow to the growing movement looking for a change in drug policy in the region.

The U.N. body says it is particularly concerned by a 2009 law in Mexico that decriminalizes possession of small amounts of cannabis, cocaine, heroin and other drugs.

“This legal act may give the wrong signal,” says a report released Wednesday by the International Narcotics Control Board, an independent body that monitors the implementation of U.N. drug control conventions.

The board said it wanted to remind the Mexican government that U.N. conventions require that the possession, purchase or cultivation of narcotic drugs be classified as a criminal offense.

The report also attacks the Argentine Supreme Court for a ruling last year that it is unconstitutional to punish the personal use of cannabis.

While not dishing out specific punishments, the narcotics control board has an important influence on drug policy, particularly in the developing world.

Activists in the bubbling drug reform movement here say that the board is taking a too conservative line, and argue that U.N. conventions do not prohibit governments from pursuing more progressive policies toward the treatment of drug addicts.

“Just putting all consumers in jail is a wrong policy. It doesn’t help society to do better and you probably destroy lives instead,” former Colombian President Cesar Gaviria told GlobalPost. “The United Nations meets every 10 years to say that in the next 10 years the world will be free of the consumption of drugs but it never happens. And the violence problems are putting Mexico and Colombia in real danger.”

Gaviria, who ruled Colombia from 1990 to 1994 and oversaw the police killing of cocaine baron Pablo Escobar, has recently joined the drug policy reform lobby — a broad-based movement that argues that the prohibition of drugs fuels violence while not stopping consumption.

The report criticized the participation of Gaviria and others in this campaign.

“The board notes with concern that in countries in South America, such as Argentina, Brazil and Colombia (and in countries in North America, such as Mexico and the United States), there is a growing movement to decriminalize the possession of controlled drugs,” it says.

"Regrettably, influential personalities, including former high-level politicians in countries in South America, have publicly expressed support for that movement. The Board is concerned that the movement, if not resolutely countered by the respective Governments, will undermine national and international efforts to combat the abuse of and illicit trafficking in narcotic drugs.”

Some international watchdogs say that with such criticism, the U.N. board is overstepping its mandate, which is to uphold the U.N. conventions rather than comment on political debates.

“They are making comments based on conservative moral perceptions and not on legal or medical considerations,” said Pien Metaal, of the Drugs and Democracy Program at the Holland-based Transnational Institute.

While the United States has historically pushed for the war on drugs at the U.N., other powers are now bringing conservative ideas to the table, Metaal said.

Among the current narcotics board members are representatives of the Russian Federation, China and Nigeria, which all support hard-line prohibitionist policies toward narcotics.

Meanwhile, the United States itself is beginning to take a more flexible line, with a growing number of states decriminalizing the possession of marijuana and legalizing the drug for medical sales.

In November, Californians will vote on a motion to fully legalize marijuana. If approved, such a law would put California at legal odds with the narcotics board.

American drug reform activists say that the United Nations needs to overhaul its drug policy institutions so the world can move forward on the issue.

“These kind of reports show the INCB is just a profoundly political organization,” said Ethan Nadelmann, director of the New York-based Drug Policy Alliance. “The board needs to be abolished.”