This undated rendering provided by DarkPulse Technologies Inc. shows a proposed border wall between Mexico and the U.S. The wall proposed by Arizona-based DarkPulse Technologies would be constructed with ballistic concrete that can withstand tampering or attacks of any kind, according to founder Dennis O'Leary. "You could fire a tank round at it and it will take the impact," he told The Associated Press.

WASHINGTON (AP) — The Trump administration has awarded more contracts to build prototypes for the wall President Donald Trump wants to build on the U.S. border with Mexico.

The prototypes announced Thursday by U.S. Customs and Border Protection are for four see-through walls. Last week, it announced contracts for prototypes for four concrete walls.

The eight prototypes will cost a total of $3.6 million and will be built in San Diego, probably during this fall.

The four companies announced Thursday are Caddell Construction Co. of Montgomery, Alabama; KWR Construction Inc. of Sierra Vista, Arizona; ELTA North America Inc. of Annapolis Junction, Maryland; and W. G. Yates & Sons Construction Company of Philadelphia, Mississippi.

The wall was a signature issue in Trump's campaign last year. He promised that Mexico would pay for it, but Mexico has refused. He is pushing Congress to fund it, but faces strong opposition from Democrats.