Homeland Security Secretary Alejandro Mayorkas traveled Monday to the makeshift camp in Del Rio, Tex., where nearly 15,000 border-crossers have arrived, and he was quickly pulled into an escalating controversy over the treatment of the mostly Haitian migrants by U.S. agents.

News cameras and photographers recorded scenes Sunday along the Rio Grande where horse-mounted Border Patrol agents attempted to grab migrants and used their animals to push them back toward Mexico. One agent is heard on video shouting an obscenity as a child jumps out of the horse’s path.

Mayorkas told reporters in Del Rio that DHS would look into the incident. By Monday evening, as criticism mounted, the department released a statement announcing more formal inquiries, which it said Mayorkas had directed after watching the videos.