TUCSON, Arizona  —  Construction has begun on vehicle barriers that will be part of a mix of fencing along the Arizona-Mexico border to discourage illegal border crossings.

The construction started Wednesday is part of a Bush administration initiative 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 be made up 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 9 miles (15 kilometers) at the western edge of a 37-mile (60-kilometer) stretch of desert in southwestern Arizona.

On Jan. 12, Homeland Security Secretary Michael Chertoff cleared the way for the work to start by waiving environmental regulations and laws impeding construction along the 2.8 million-acre (1.1-million-hectare) Barry M. Goldwater bombing range.

Environmentalists have criticized the fencing and barrier plans, saying that will not stop people in search of jobs but will be a step toward destroying a fragile portion of southern Arizona's desert.

The initial construction phase could take a few months.