The Mexican army said the tunnel was found Thursday after authorities received an anonymous call in the border city of Nogales, Sonora, south of Arizona. U.S. law enforcement officials confirmed that the Mexican military had discovered the football field-long tunnel with elaborate electricity and ventilation systems.
U.S. Border Patrol spokesman Victor Brabble said the tunnel did not cross into the U.S.
The army said the anonymous caller was reporting gunmen standing outside a two-story house in a hilly neighborhood near the international bridge where motorists travel between Mexico and the United States.
Inside the house, soldiers discovered a fake wall inside a storage closet under a staircase that led to a dark room with buckets and clothes. After lifting a drain cover in that room, soldiers found another staircase at the entrance of the tunnel that went 16 feet underground and measured a yard in diameter. Light bulbs lit the underground passage and pipes stretched across the 120-yard tunnel that Mexican army officials believe was built to smuggle drugs.
It was unclear whether officials made any arrests, but the house where the tunnel was found was seized by the local government. Military officials did not say how long they believed the tunnel had been under construction, but authorities say it can take six months to a year to build such a passage.
Sophisticated secret tunnels stretching across the international border have become increasingly common as drug cartels invent new ways to smuggle enormous loads of heroin, marijuana and other drugs into U.S.
More than 70 such tunnels have been found since October 2008, most of them concentrated along the border in California and Arizona. In Nogales, Arizona, smugglers tap into vast underground drainage canals.
AP correspondent Brian Skoloff contributed to this report from Phoenix, Ariz.