The FBI is investigating a shootout that wounded two Mexican guards near a border wall construction site in California last year, The Washington Post reported.

The shootout reportedly occurred on July 1, 2019, when the guards were ambushed while protecting materials and equipment from a Texas-based construction contractor. The guards returned fire and sustained several gunshot wounds, the Post reported.

The incident has reportedly led to scrutiny of the protocols for the Mexican security companies that are hired to protect the southern side of border wall construction sites.

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According to the documents obtained by the Post, the guards did not violate existing protocols, and the primary contractor later revised its protocols to include screenings for Mexican security personnel.

The security company the guards worked for was also not vetted by the U.S. Army Corps or Customs and Border Protection (CPB), unlike the companies that are contracted to protect the U.S. side of the construction site.

“When NSSP personnel were interviewed, they stated they were all prior Mexican National Army and had been trained on when to use deadly force,” the document reportedly states, referring to the Mexico-based firm where the guards worked.

The Hill has reached out to the FBI and CBP for comment.

Acting Homeland Security Secretary Chad WolfChad WolfDHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Judge blocks some asylum restrictions, rules Chad Wolf serving as DHS secretary likely unlawful DHS asks Schiff to reconsider expanded probe after whistleblower complaint, declines additional interview requests MORE announced last month that the administration had completed 100 miles of new border barriers under President Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE.

The administration has sought to build 450 miles of new border barriers by the end of 2020.

Trump declared a national emergency at the U.S. border in February 2019, leading him to divert $7.2 billion in military funds to go to border wall construction.

House Democrats recently raised alarms about the administration seeking to redirect another $7.2 billion in military funding to the border wall.