US-Mexico border tunnels remain unfilled, raise security fears

SAN DIEGO (AP) -- Key entrances have been plugged in some of the biggest tunnels used to smuggle people and drugs across the U.S.-Mexico border but the passageways remain largely intact, raising concerns that smugglers might reuse them, according to a published report.

Critics say the unfilled tunnels pose an unnecessary national security risk.

Dozens of tunnels have been discovered underneath the border. Smaller passages are easily destroyed, but larger, more elaborate shafts require costly amounts of material and expertise to fill, authorities say. The task is further complicated if the tunnels run under private property.

Seven of the largest tunnels have yet to be filled in, including the so-called Grande Tunnel found in January 2006 that extends nearly a half-mile from San Diego to Tijuana, the Los Angeles Times reported Tuesday.