MEXICO CITY — Voters in Colorado and Washington state who approved the recreational use of marijuana Tuesday sent a salvo from the ballot box that will ricochet around Latin America, a region that’s faced decades of bloodshed from the U.S.-led war on drugs.

Experts said the moves were likely to give momentum to countries such as Uruguay that are marching toward legalization, to undercut Mexican criminal gangs and to embolden those who demand greater debate about how to combat illegal substances.

“The trend is toward legalization,” said Jorge G. Castaneda, a former Mexican foreign minister who’s an advocate for decriminalization.

The decision by voters in Colorado and Washington to legalize marijuana for recreational use puts those states — the first to approve outright legalization — at loggerheads not only with the federal government but also with global treaties that label marijuana a controlled substance.

Taking a lesser step, Massachusetts voters approved a measure that allows the medical use of marijuana, joining 17 other states and the District of Columbia in permitting such limited usage.

U.S. diplomats in Latin America said Wednesday that President Barack Obama would hold firm against efforts to soften drug laws.

But contradictory policies at the state and federal levels in the United States may throw the door open to more intense debate about U.S.-led pressure to respect international narcotics treaties.

“Politically and symbolically, this is really powerful. My guess is that this will accelerate some countries’ efforts to have a legal marijuana regime,” said Alejandro Hope, a former ranking official in Mexico’s civilian intelligence service who studies the economic impact of marijuana smuggling in Mexico.

Uruguay, a small South American nation led by a former leftist guerrilla, has moved ahead since August on a proposal to legalize marijuana under a government monopoly.

“Chile also has a bill before its Congress. I’m guessing that Argentina may also follow suit. This will go from south to north,” Hope said.

He added, however, that change would come over years, not months.

Experts said nations — or states within nations — couldn’t easily buck global treaties that included marijuana as a criminal substance.

“It’s a direct breach of the 1961 U.N. convention on narcotic drugs,” said Martin Jelsma, a Dutch scholar on drug control laws at the Transnational Institute, a center in the Netherlands that advocates for less punitive global drug policies.

Jelsma said nations and states “will have to find a way to reconcile” their laws with the global treaty, which has some 190 signatories.