Shooter Targets Texas Border Patrol Agents in Ambush, Shot Dead Outside Building

A man armed with a rifle and tactical gear allegedly attempted to ambush law enforcement as they showed up for work at a Border Patrol facility in Texas ... he opened fire, then got shot and killed.

The fatal exchange of gunfire went down Monday morning in McAllen ... according to the Department of Homeland Security.

We're told Border Patrol agents and local police helped neutralize the shooter, who opened fire at the entrance of a United States Border Patrol sector annex.

DHS says two officers and a Border Patrol employee were injured in the shooting ... including one who was shot in the knee. All three have gone to the hospital.

We're told the FBI is now investigating the shooting ... and photos show the gunman on the ground outside a building, with evidence markers surrounding his body.