The two events were not related. It was not in response to the latest school shootings in the US that Mexican politicians moved to change the legislation. But the timing was certainly symbolic.

Ironically for a country awash with hundreds of thousands of illegal firearms, Mexico has some of the most stringent gun laws in Latin America.

Mexicans do have the right to own a registered gun in their home, but only the military, police and citizens with federal permits can carry arms outside the home.

Obtaining that licence costs $150 (£93) and involves rigorous checks. Consequently, many ordinary Mexicans who want to carry a weapon simply buy on the black market.

Since the Mexican government shut down the last private gun shop in the 1990s, there is just one legal gun store in the entire country, located in Mexico City and controlled by the military.

This latest piece of legislation was aimed at stemming the flow of magazines for automatic weapons into the country by closing a longstanding legal loophole.

Senator Arturo Zamora of the ruling PRI party introduced the measure to parliament saying: "The traffic of magazines for high-calibre weapons is in the hands of criminal organisations."

"These magazines pose a threat to society. They are not being brought into country with the aim of protecting people but rather to be used in crimes such as extortion, kidnapping and murder."

As the US grapples with the implications of the shootings in Newtown, there has been relatively little mention of the impact the country's lax gun laws have had on its southern neighbour.

Last year a US Senate report, submitted by the Democratic senator leading the push for greater gun control, Dianne Feinstein, said as many as 70% of the guns in the hands of the Mexican drug cartels came from the US.

Two years earlier, the number cited had been even higher, at about 90%.

For the pro-gun lobby, however, the statistics were inaccurate and the report fundamentally flawed.

The figure was based on some 30,000 guns confiscated by the Mexican authorities and submitted to the US Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) for tracing.

Critics of Senator Feinstein's report say there are tens of thousands of weapons which were not handed over for tracing and many more still in circulation in Mexico whose origins are unknown.

"The single biggest supplier of firearms to the Mexican criminals is the US government through our sales to the military and the police," argues Robert Farago of the pro-gun online magazine The Truth about Guns.

Those firearms are "fully-automatic assault rifles", says Mr Farago, which "then seep to the cartels. They also have weapons coming in from China and Eastern Europe."

Fast and Furious

One particular episode involving US weapons in Mexico has created more tension between the two countries over the issue than any other.

In a botched sting operation by the ATF called Fast and Furious, US authorities lost track of some 1,400 weapons they were hoping would to lead them to drug kingpins. Instead the guns simply ended up arming Mexican gangs, particularly the Sinaloa Cartel.

"Fast and Furious" weapons have turned up in violent crime scenes across Mexico.

Now a Republican Senator from Iowa, Charles Grassley, has called for an investigation into whether guns from the bungled operation were used in a shoot-out earlier this year in which a 20-year-old beauty queen, Maria Susana Flores Gomez, was killed.

For pro-gun commentator Robert Farago, Fast and Furious is an example of where the problem lies.

"The idea that US gun laws are in any way impacting the availability of firearms in Mexico is ridiculous," he says. "It's not United States' gun stores they need to worry about."

Nevertheless, the 2011 Senate report concluded that the private sale of military-style weapons was "arming Mexico's drug trafficking organisations at an alarming rate", and called for the Assault Weapons Ban to be reinstated.

Those calls have turned into urgent demands from some quarters in the wake of the massacre at Newtown.

In Mexico, politicians and members of civil society have long made a link between US gun laws and the firepower of Mexico's cartels.

Asked whether greater gun control north of the border would improve security in Mexican communities, PRI Senator Arturo Zamora was emphatic: "Definitely it would, yes. In June, the Defence Ministry stated that in the last six years, it confiscated more than 12 million cartridges of different calibres."

Tighter US gun laws, he says, would immediately help to curb the illegal traffic of so many bullets and weapons into Mexico.

Needless to say, US gun enthusiasts vehemently disagree.

"It's absolutely laughable," says Robert Farago of the senator's argument.

"If anything, Mexicans should be copying our gun laws and Second Amendment rights. What Mexicans need are more magazines, more guns, more bullets in the hands of law-abiding citizens."

Most law-abiding Mexicans, however, believe more guns are the last thing the country needs.