(wapo) Drug cartel violence in Mexico is quickly spilling south into Central America and is threatening to destabilize fragile countries already rife with crime and corruption, according to the United Nations, U.S. officials and regional law enforcement agents. The Northern Triangle of Central America -- Guatemala, El Salvador and Honduras -- has long been a major smuggling corridor for contraband heading to the United States. But as Mexican President Felipe Calderón fights a U.S.-backed war against his nation's drug lords, trafficking networks are burrowing deeper into a region with the highest murder rates in the world. The Mexican cartels "are spreading their horizons to states where they feel, quite frankly, more comfortable. These governments in Central America face a very real challenge in confronting these organizations," said David Gaddis, chief of operations for the U.S. Drug Enforcement Administration. U.S. attention has mostly focused on Mexico. But the homicide rate there -- 14 for every 100,000 residents -- is dwarfed by the murder statistics in the Northern Triangle, where per-capita killings are four times higher and rising. In El Salvador, the region's most violent country, homicides jumped 37 percent last year, to 71 murders per 100,000 residents, as warring gangs vied for territory and trafficking routes.