An active shooter armed with tactical gear and a rifle opened fire upon Border Patrol agents as they arrived at a Border Patrol annex facility in McAllen, Texas, in the Rio Grande Valley on Monday.

Agents and local police returned fire and killed the gunman. No federal agents were hit, but one McAllen police officer was struck. Law enforcement sources say the officer is in stable condition.

Law enforcement believes the attack was a purposeful ambush targeting Border Patrol officials.

This is a developing story. Check back soon for updates.