Leftist lawmakers on Thursday proposed allowing the sale of marijuana within Mexico City, seeking to join Uruguay and the U.S. states of Washington and Colorado in creating legal markets for the drug.

The bill is vague on many key points and faces legal hurdles that may be impossible to overcome but it creates at least the possibility of an island of legalization of one drug in a nation that has been devastated by the fallout from the U.S.-backed fight to stop the northbound flow of recreational narcotics.

Most legislators in the Mexico City assembly haven't said whether they back the proposal, but the local legislature controlled by the leftist Democratic Revolution Party is the most liberal in Mexico and has previously legalized abortion and gay marriage. Mayor Miguel Angel Mancera supports the plan.

Approval could force a legal showdown with the federal government, which would have to decide whether to effectively override the local law by enforcing federal laws barring drug trafficking, challenging the city law in the courts, or both. President Enrique Pena Nieto has come out against drug legalization, which he says will not reduce the violence that has left tens of thousands dead across the country over the last seven years.

The initiative would allow stores in the city of 8 million to sell marijuana in amounts up to 5 grams. The bill envisages a limit on the cumulative amount that each business could sell, but doesn't specify what that could be. Since 2009, Mexican federal law has allowed the possession of no more than 5 grams of marijuana, about four joints, for personal use, but it still requires the arrest of anyone caught buying or selling any amount.

The bill is silent on the number of stores that would be allowed, or how marijuana sales would be regulated, taxed and enforced.

The sponsors are also asking allies in the federal congress to push forward with a law that would legalize marijuana production throughout the country, effectively providing a source for any legal pot shops. That federal bill, which also proposes allowing Mexicans to legally possess up to 30 grams of marijuana, is almost certain to go nowhere in the national legislature, which is dominated by Pena Nieto's party and the conservative National Action Party.

The proposal in Mexico City's assembly also doesn't specify if it would allow only city residents to buy pot.

The bill's sponsors acknowledged many details remain to be worked out, but called it an important step in fueling Mexican discussion about marijuana legalization, a topic that has gained major momentum with the legalization of sales in Colorado, Washington and Uruguay. Many Mexicans find it increasingly absurd that their country is spending money and law-enforcement effort to keep marijuana from crossing the northern border into a country where it is already legal for millions of people.

While the Mexico City bill would have little to no effect on the larger cross-border drug trade, sponsor Vidal Llerenas called it a move toward allowing authorities to focus on more serious crimes.

"Mexico needs to lead a discussion about how we can deal with drugs in a different way," Llerenas said.

The initiative "puts Mexico City in a leading position in Latin America," said Jorge Castaneda, a former Mexican foreign minister. "Rather than continue fighting a war that makes no sense, now we are joining a cutting-edge process," he added.

Mexico has seen a slight increase in drug use in the last few years, according to health authorities and marijuana remains the most commonly used drug.

Mexican Assistant Interior Secretary Roberto Campa said that so far there is no plan to challenge the initiatives, but stressed that both require a deeper analysis before their approval.

U.S. President Barack Obama has said it is not his administration's priority to prosecute marijuana use and has allowed the Colorado and Washington plans to proceed without federal action against them.

Uruguay last year became the first country to legalize the production and commercialization of marijuana nationwide.

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