Construction began Wednesday on vehicle barriers that will be part of a mix of fencing along the Arizona-Mexico border to discourage illegal border crossings.
The construction is part of a Bush administration initative announced last year that aims to provide a mix of high-tech virtual fencing and a traditional physical barrier.
The first phase of construction will consist primarily of concrete-filled vertical tubes set into the ground to prevent vehicles from entering.
Department of Homeland Security spokesman Russell Knocke said some portions of the barrier may also contain traditional fencing.
The first phase will be placed along nine miles at the western edge of a 37-mile stretch of desert in southwestern Arizona.