(CBSNEWS) – Defense Secretary Jim Mattis is preparing an order that would send approximately 800 U.S. troops to the border, CBS News’ David Martin has confirmed, as President Trump’s frustration builds over the caravan of migrants approaching the U.S.

That is in addition to the National Guard troops sent earlier this year, although it is not yet clear whether the additional troops will also be National Guard or active duty military members, Martin reports. In April, the Pentagon authorized 4,000 National Guard troops to head to the southern border to aid U.S. and Customs and Border Protection. CNN first reported the Pentagon’s intent to sign off on more troops.

The additional troops will not have any authority to apprehend illegal immigrants but will be able to erect barriers and provide reconnaissance searching for illegal border crossers. It’s not yet exactly clear where they will deploy.

The move comes as Mr. Trump claimed on Twitter Thursday morning he is “bringing out the military for this National Emergency.” The president, who has long blasted illegal immigration and touted the importance of border security, has focused on the caravan in recent days leading up to the midterms, calling the matter a great Republican issue ahead of the midterms.

*READ MORE AT CBSNEWS.COM*