( CNN ) -- Federal drug agents discovered a 240-yard-long tunnel underneath the U.S.-Mexico border , and they suspect it was used to smuggle drugs into Arizona for sale in the United States , officials said Thursday . The `` sophisticated drug smuggling tunnel , '' which runs 55 feet below ground , begins in an ice plant in San Luis Rio Colorado , Sonora , Mexico , and ends inside a one-story , nondescript building in San Luis , Arizona , according to the U.S. Drug Enforcement Administration . Report : Focus on cops , not military . Investigators started watching the building in January `` after observing possible suspicious activity that indicated the site was being used as a potential stash location , '' the DEA said . Arizona police found 39 pounds of methamphetamine inside a pickup truck stopped on Interstate 95 on July 6 , which led them back to the San Luis , Arizona , building , the DEA said . They got a search warrant with that information . Police in Arizona arrest 20 , dismantle drug trafficking cell of Sinaloa Cartel . No drugs were found in the search of the ice plant or the building on the U.S. side , just bags and barrels of dirt , the DEA said . Three unnamed suspects have been arrested in connection with the tunnel , the DEA said . Interior Border Patrol stations closed . `` The recent discovery of this sophisticated drug smuggling tunnel is yet another reminder of how desperate these criminal organizations are and the extent they will go to further their drug dealing operations and endanger the security of our citizens , '' said Doug Coleman , the special agent in charge of the DEA 's Phoenix , Arizona , office . In small-town USA , business as usual for Mexican cartels .
`` Sophisticated drug smuggling tunnel '' runs from an ice plant in Mexico , the DEA says . Arizona police traced 39 pounds of methamphetamine in a truck to the tunnel , agents say . Comment: