Last year, about 1.1 million people were arrested crossing the border illegally from Mexico, more than a third of them through the heavily trafficked desert corridor south of Tucson, Arizona.

The Border Patrol said the system, which is being built by aerospace giant Boeing under a contract estimated at some $2 billion, is a necessary step to close the border to illegal entrants and allow agents to promptly identify and capture illegal immigrants and drug smugglers.

Information captured by the towers -- including live images giving GPS locations of any intruders -- will be streamed live via satellite from command centers in Tucson and Sells to Border Patrol agents with laptops patrolling nearby.

Eventually it will be integrated into a wider network, including a fleet of Predator B unmanned surveillance drones.

"We need to have eyes on what's happening here," said Tucson sector Border Patrol spokesman Jesus Rodriguez. "We are not placing the town under surveillance, but we wi