SAN DIEGO — Top U.S. border officials expect cartels to build more tunnels from Mexico to the United States and increasingly rely on drones for surveillance operations as the 400 miles of new border wall makes it harder to smuggle people and drugs into the country.

Transnational criminal organizations have long used tunnels and drones at the southwest border, but senior Border Patrol officials across the country are bracing for more activity as new 30-foot-tall barrier wall goes up in areas that have long been easy for criminals to cross.