The White House has criticised images that show a US border patrol agent on horseback appearing to use a whip to threaten migrants.
Press secretary Jen Psaki on Monday called the scenes “horrific” but added that more information was needed.
In both footage and photos, agents are shown confronting migrants near a camp by the Rio Grande river in Del Rio, Texas as they try to cross the US border from Mexico.
In recent days, the mostly Haitian migrants have been crossing back and forth between Ciudad Acuna and the camp – hosting at least 10,000 migrants– to buy food and water, currently in short supply on the US side.
Some images show one agent riding a horse with what appears to be a whip or reign and grabbing one of the migrants by their t-shirt.
According to the El Paso Times, an agent swung his whip and charged his horse at those trying to enter the country, shouting: “Let’s go! Get out now! Back to Mexico”.
Reuters also reported that a law enforcement officer in the same area whipped a lasso close to the face of a migrant although it is unclear if this was the same agent.
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Asked about the scenes at the daily White House news briefing, Ms Psaki said: “I have seen some of the footage. I don’t have the full context.
“I can’t imagine what context would make that appropriate, but I don’t have additional details. I don’t think anyone seeing that footage would think it’s acceptable or appropriate.”
The White House press secretary was pressed over the images and was asked if the use of whips was something the Biden administration permitted.
Ms Psaki called the footage “horrible to watch”, but added that before she could comment further the administration needs “to get more information”.
Asked if the agent should be fired, she said: “Of course they should never be able to do it again.”
Meanwhile, in a statement on Monday night, the US department of homeland security said the agency “does not tolerate the abuse of migrants in our custody and we take these allegations very seriously.”
The statement added that the custom and border protection’s office of professional responsibility “is investigating the matter and has alerted the DHS office of inspector general.”
Earlier on Monday, during a visit to the camp in Del Rio, homeland security head Alejandro Mayorkas, told a reporter they were “assuming the facts”, when asked about the images.
Mr Mayorkas went on to say it was possible the agent was simply holding a long rein rather than a whip.
“To ensure control of the horse, long reins are used but we are going to investigate the facts to ensure that the situation is as we understand it to be and if it’s anything different, we will respond accordingly,” he said.
Mr Mayorkas was joined by border patrol chief Raul Ortiz, who defended his agency’s use of horses, saying they “play an integral part in the security response”.
“We do not know who are the smugglers or who are the migrants, so it’s important that those border patrol agents maintain a level of security for both themselves and for the migrant population as they were trafficking back and forth,” Mr Ortiz added.
As for whether an agent was using a whip, he said “we’ll certainly look into the matter” to ensure agents are not engaging in “unacceptable” activity.