A makeshift cart with containers is seen at a suspected drug tunnel under construction during a media tour by Mexican Army in Tijuana April 7, 2015. Mexican soldiers foiled the construction of a suspected drug tunnel underneath a house near the U.S. border, arresting nine people and impounding a truck used to clear debris, the Army said on Tuesday. Wired with lights, the tunnel was being built next to the Tijuana border crossing, south of San Diego, California, and near a Mexican air force installation as well as a regional federal police facility. (Photo by Reuters/Stringer)

Soldiers stand guard outside a house, where a suspected drug tunnel under construction was located, during a media tour by Mexican Army in Tijuana April 7, 2015. (Photo by Reuters/Stringer)

A reporter is seen at a suspected drug tunnel under construction during a media tour by Mexican Army in Tijuana April 7, 2015. (Photo by Reuters/Stringer)

A policeman (L) checks the access to a suspected drug tunnel under construction, which is located inside a wardrobe, during a media tour by Mexican Army in Tijuana April 7, 2015. (Photo by Reuters/Stringer)

Soldiers inspect the entrance of a cross border tunnel at a warehouse in Tijuana, July 12, 2012. (Photo by Jorge Duenes/Reuters)

A soldier stands next to a federal agent (R) inspecting the entrance to a tunnel under construction found by soldiers at a recycling plant at the Otay Mesa industrial park in Tijuana, July 12, 2012. (Photo by Reuters/Stringer)

Law enforcement officers inspect a drug tunnel found in a warehouse in Otay Mesa, California, April 3, 2014. U.S. federal agents uncovered two drug-smuggling tunnels underneath the U.S.-Mexico border, both surfacing in San Diego-area warehouses and equipped with rail systems for moving contraband. The discovery led to the arrest of a 73-year-old woman accused of running one of the warehouses connected to a drug smuggling operation. (Photo by Reuters/Immigration and Customs Enforcement)

A Mexican soldier looks down into a tunnel found under the Mexico-U.S. border in Tijuana, November 30, 2011. The tunnel, equipped with electric rail cars, ran from California from Mexico and authorities from both countries seized more than 32 tons of marijuana. (Photo by Jorge Duenes/Reuters)

An underground tunnel next to the U.S.-Mexico border is remediated with concrete in Arizona, May 22, 2014. The incomplete tunnel was roughly 140 feet long and typically used to smuggle drugs, according to U.S. Border Patrol. The tunnel will take 6 concrete trucks to fill so that there is no sinkhole, collapse or possible use in the future. (Photo by Samantha Sais/Reuters)

A view of the entrance to a tunnel under construction found by soldiers at a recycling plant at the Otay Mesa industrial park in Tijuana, July 12, 2012. (Photo by Reuters/Stringer)

Members of the media wait for their turn to film the entrance to a tunnel under construction found by soldiers at a recycling plant at the Otay Mesa industrial park in Tijuana, July 12, 2012. (Photo by Reuters/Stringer)

An underground drug smuggling tunnel from Mexico into Nogales, Arizona, in a photo released March 1, 2012. (Photo by Reuters/Immigration and Customs Enforcement)

An image of the Virgin of Guadalupe is seen in a tunnel, nearly a mile long running into California from Tecate, Mexico, December 4, 2007. (Photo by Jorge Duenes/Reuters)

A soldier looks into a tunnel found under the Mexico-U.S. border in Tijuana, November 30, 2011. (Photo by Jorge Duenes/Reuters)

A sophisticated smugglers' tunnel, fitted with lights, water pumps and a ventilation system, running under the Arizona border from Mexico found by U.S. border police, May 9, 2011. (Photo by Reuters/U.S. Border Patrol)

Packs of marijuana are stored in a tunnel in Tijuana, November 3, 2010. (Photo by Jorge Duenes/Reuters)

Local police stand guard near a hole that exposed a tunnel in Tijuana August 2, 2011. Authorities discovered the tunnel near another tunnel that had been sealed two years ago. (Photo by Jorge Duenes/Reuters)

Plywood shoring with a built-in makeshift ladder at the entrance to a drug smuggling tunnel from Mexico uncovered by the U.S. Border Patrol in Nogales, Arizona. Photo released November 22, 2011. (Photo by Reuters/U.S. Customs and Border Protection)

A soldier opens the access to a tunnel as others stand guard near packages containing marijuana during a presentation to the media in Tijuana, November 16, 2011. (Photo by Jorge Duenes/Reuters)

The entrance to a long tunnel inside a warehouse near the Mexican border in Otay Mesa, California, November 3, 2010. (Photo by Nelvin C. Cepeda/Reuters/San Diego Union-Tribune)

A Mexican soldier flashes his torchlight inside a tunnel the length of six football fields, in Tijuana, November 3, 2010. (Photo by Jorge Duenes/Reuters)

Packages containing marijuana sit next to a tunnel found under the Mexico-U.S. border in Tijuana, November 29, 2011. (Photo by Reuters/Mexico Police)

A journalist climbs the shaft of a cross border tunnel located by the Mexican army at a warehouse in Tijuana July 12, 2012. (Photo by Jorge Duenes/Reuters)

A journalist crawls in a cross border tunnel located by the Mexican army at a warehouse in Tijuana July 12, 2012. (Photo by Jorge Duenes/Reuters)