A huge rise in gun seizures in Mexico, which have gone up 16-fold over the last four years, indicates the failure of customs authorities to stop weapons entering the country — and not just from the U.S.

Mexico’s Ministry of Defense seized more than 83,000 weapons in 2010, according to statistics quoted by El Universal; a vast increase on the less than 6,000 seized in 2007.

Meanwhile, as an investigation by Milenio revealed, Mexican customs agents (Servicio de Administracion Tributaria – SAT) have only managed to confiscate a tiny fraction of all weapons smuggled into the country. In recent years the Federal Police have been far more successful in confiscating illegal arms than the customs officers.

The consequences of the SAT’s failure are easy to see. Tens of thousands of weapons enter the country, are used against citizens and law enforcement officers, and some are eventually confiscated by police forces in raids or other high risk operations.

The weakness of the SAT worries the U.S. government, which maintains a SAT training center as part of the Department of Homeland Security in El Paso Texas. The U.S. Customs and Border Patrol has recently stepped up training of SAT staff, including increased courses in the detection of smuggled money, narcotics and firearms, as well as the use of canines, reported Milenio.

Since 2007, the U.S. has spent nearly $5 million under the Merida Initiative to help modernize the SAT, and has been involved with cross-border initiatives aimed at increasing bilateral cooperation. Despite this influx of U.S. dollars, border seizures have fallen in some crossing points, according to Milenio, leaving domestic law enforcement agencies to pick up the slack.

Weapons proliferation is a complex problem that cannot be easily solved, even with improved border inspections. An estimated 2,000 weapons cross the border illegally into Mexico·every day, according to Milenio. Although the country which has some of the strictest gun ownership laws in the world, everything from AK-47 to anti-aircraft guns are smuggled across the border.

Many have fingered the United States as the main source of illegal weapons in Mexico, but the problem does not only exist on the U.S. border. Guatemala is also an important source of weapons for Mexico’s armed groups. As InSight has reported, weapons seized from Mexican drug gang the Zetas have been traced back to the Guatemalan military. Many cartel members reportedly carry arms imported from Romania and China.

The U.S. Government Accountability Office (GAO) said in June 2009 that 90 percent of arms found in Mexico originated in the United States. However, this figure was derived only from traceable weapons, which accounted for less than 12 percent of the GAO’s figures, according to Stratfor.

Furthermore, as Stratfor pointed out, many of the weapons confiscated in Mexico are not available for purchase in the United States. This includes military-grade hand grenades, rocket-propelled grenades, automatic assault rifles and light machine guns. Due to heavy military security in the U.S., it is likely the majority of such weapons originate in countries such as China, Guatemala or even South Korea. The head of the U.S. army’s Southern Command, General Douglas Fraser, has testified that over 50 percent of military grade weapons in Mexico come from Central America.

While gun seizures in Mexico have increased massively during Calderon’s time as president, it is not clear whether this indicates improved policing or just higher arms smuggling. What is clear is that the U.S. border is not the only frontier that needs to be fortified.