The four called for the Organization of American States to study the impact of the Colorado and Washington votes and said the United Nations’ General Assembly should hold a special session on the prohibition of drugs by 2015 at the latest.

Last week, the most influential adviser to Mexico’s president-elect, who takes office Dec. 1, questioned how the country will enforce a ban on growing and smuggling a drug that is now legal under some U.S. state laws. The Obama administration has yet to make clear how strongly it will enforce a federal ban on marijuana that is not affected by the Colorado and Washington votes.

“It has become necessary to analyze in depth the implications for public policy and health in our nations emerging from the state and local moves to allow the legal production, consumption and distribution of marijuana in some countries of our continent,” Mexican President Felipe Calderon said after a meeting with Honduran President Porfirio Lobo, Costa Rican President Laura Chinchilla and Prime Minister Dean Barrow of Belize.

Marijuana legalization by U.S. states is “a paradigm change on the part of those entities in respect to the current international system,” Calderon said.

Mexico has seen tens of thousands of people killed over the last six years during a militarized government campaign against the country’s drug cartels.

President-elect Enrique Pena Nieto has promised to shift Mexico’s focus to preventing violence against ordinary citizens, although he says he intends to keep battling cartels and is opposed to drug legalization. Guatemala’s president has advocated the international legalization of drugs.

Monday’s statement by the four leaders “is an important indicator of the desire to engage in a more robust discussion of policy,” said Eric Olson, associate director of the Mexico Institute at the Woodrow Wilson International Center for Scholars in Washington.

The call by the four presidents was welcomed by marijuana activists in the U.S. Forcing international review of drug policies was a stated goal of the campaigns for legalization in Colorado and Washington.

“Marijuana prohibition in this country has been detrimental — but it’s been absolutely catastrophic to our southern neighbors,” said Dan Riffle, an analyst and lobbying for the Marijuana Policy Project, a Washington, D.C.-based advocacy group that largely financed the two campaigns.

Mexico is one of the primary suppliers of marijuana to the U.S., while Honduras and Belize are important stops on the northward passage of cocaine from South America. Costa Rica is seeing increasing use of its territory by drug traffickers.

Luis Videgaray, head of Pena Nieto’s transition team, told Radio Formula on Wednesday that the votes in the two states complicated his country’s commitment to stopping the growing and smuggling of marijuana.

“Obviously we can’t handle a product that is illegal in Mexico, trying to stop its transfer to the United States, when in the United States, at least in part of the United States, it now has a different status,” Videgaray said.

Videgaray stopped short of threatening to curtail Mexican enforcement of marijuana laws, but his comments appeared likely to increase pressure on the Obama administration to strictly enforce U.S. federal law, which still forbids recreational pot use.