U.S. authorities in Mexico charged with stemming the flow of U.S. weapons to drug cartels have been hampered

U.S. authorities in Mexico charged with stemming the flow of U.S. weapons to drug cartels have been hampered by shortfalls in staffing, agents with limited Spanish skills and the difficulty of recruiting new agents to the dangerous posting because they can't officially carry weapons, current and former staff members say.

Facing new accusations that investigators with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives allowed buyers to funnel high-powered assault weapons into Mexico, a senior agent posted to Mexico before 2010 said the agency had not fielded the resources necessary to block mass movements of weapons across the Southwest border.

These movements have come under scrutiny amid revelations that ATF investigators delayed for months the arrests of suspected cartel gun buyers, allowing the flow of hundreds of weapons to Mexico in the hope of catching bigger buyers. The policy has outraged many agents and prompted a Senate investigation.