Acting Pentagon chief Patrick Shanahan said Monday he had authorised $1 billion to build part of the wall sought by President Donald Trump along the United States-Mexico border.

The Department of Homeland Security asked the Pentagon to build 92 kilometers of 5.5-meter fencing, build and improve roads, and install lighting to support Trump's emergency declaration as concerns the border.

In February, President Donald Trump declared a national emergency in order to funnel billions of dollars to wall construction.