Homeland Security investigates border patrol’s treatment of Haitian immigrants.

Images and video of U.S. Border Patrol agents on horseback grabbing and chasing down Haitian migrants at the U.S.-Mexico border have prompted the Department of Homeland Security to launch an investigation into the matter, the agency said on Twitter.

On Monday, D.H.S. said in a tweet that it has reviewed footage emerging from the border and takes the allegations of abuse against migrants “very seriously.”

“The footage is extremely troubling, and the facts learned from the full investigation, which will be conducted swiftly, will define the appropriate disciplinary actions to be taken,” D.H.S. said.

The Office of Professional Responsibility will lead the probe, and it will also deploy personnel to the border, where thousands of Haitians have poured into the town of Del Rio, Texas, in recent days, living in a temporary camp and hoping to seek asylum in the United States.

The announcement of the investigation follows the publication of scenes from along the Rio Grande depicting what appears to be Border Patrol officials mounted on horseback chasing, grabbing and intimidating migrants, using their horses to physically block them from crossing further into the United States. In one video recorded by Al Jazeera English, an agent can be heard using an expletive as he uses his horse to block and steer migrants back toward the river.

Jen Psaki, White House press secretary, called the footage “horrific.”

Speaking from Del Rio, Alejandro N. Mayorkas, the secretary of the U.S. Department of Homeland Security, issued a warning to Haitians trying to enter the United States, saying that protection has been extended for those who arrived before July 29. That protection does not extend to new arrivals.

“We are very concerned that Haitians who are taking this irregular migration path are receiving false information that the border is open or that temporary protected status is available,” he said during a news conference. “I want to make sure that it is known that this is not the way to come to the United States.”