CIUDAD ACUNA, Mexico (Reuters) — The White House on Monday criticized the use of horse reins to threaten Haitian migrants after images circulated of a U.S. border guard on horseback charging at migrants near a riverside camp in Texas.

The mostly Haitian migrants in recent days have been crossing back and forth between Ciudad Acuna in Mexico and the sprawling camp across the border in Del Rio to buy food and water, which was in short supply on the U.S. side.

A video showing a border guard apparently threatening migrants with the cords was shared on social media.

“I don’t think anyone seeing that footage would think it was acceptable or appropriate,” White House spokeswoman Jen Psaki told reporters.

“I don’t have the full context. I can’t imagine what context would make that appropriate,” she added.

Former Acting Secretary of the Department of Homeland Security Chad Wolf said on NewsNation’s The Donlon Report that border patrol agents are doing what they were hired to do.

“We hired the border patrol to make sure we keep illegal individuals and activity out of the country and that we push folks to legal ports of entry,” Wolf said. “If folks continue to cross that border illegally then they’re going to encounter border patrol in a variety of different ways, particularly if folks are trying to evade border patrol. They have a mission to apprehend those individuals and make sure that they are brought into custody one way or another.”

Yet, some on social media commented that the image of fleeing Black men chased by white officers on horseback had echoes of the historical injustices suffered by Black people in the United States.

U.S. Border Patrol Chief Raul Ortiz said the incident was being investigated to make sure there was not an “unacceptable” response by law enforcement. He said officers were operating in a difficult environment, trying to ensure the safety of the migrants while searching for potential smugglers.

Department of Homeland Security Secretary Alejandro Mayorkas said the long reins are used by mounted officials to “ensure control of the horse.”

“But we are going to investigate the facts,” he said during a news conference in Del Rio.

The camp under a bridge spanning the Rio Grande has become the latest flashpoint for U.S. authorities seeking to stem a flow of migrants fleeing gang violence, extreme poverty and natural disasters in their home countries.

The camp was a temporary home to more than 12,000 migrants, though Texas Gov. Greg Abbott said the number reached as high as 16,000 on Saturday. Many had traveled from as far south as Chile, hoping to apply for asylum in the United States.

On Monday, as temperatures soared to 104 degrees Fahrenheit, migrants complained about continued shortages of food and water in the camp. Some of those crossing back into the U.S. could be seen balancing large bags of ice on their heads as they waded through the water.

During the day hundreds of migrants had returned to the Mexico side, including families with young children, hoisting backpacks, suitcases and belongings in plastic bags above their heads.

“This treatment they are giving is racism, because of the color of our skin,” said Maxon Prudhomme, a Haitian migrant on the banks of the Rio Grande in Mexico.

As the sun was setting, about 200 migrants on the Mexican side bivouacked in a field by the river, flattening cardboard boxes and unfurling blankets to sleep under a cluster of trees.

Some migrants said they returned to Mexico in search of food and water, while others crossed due to fears they would be deported back to Haiti on flights organized by U.S. authorities.

The first flights carrying migrants landed in Port-au-Prince on Sunday from the Del Rio camp arrived in Haiti on Sunday, with at least three more due to make the journey on Monday, according to flight-tracking website FlightAware.

On Monday, the U.S. Secretary of State Antony Blinken spoke by phone with Haitian Prime Minister Ariel Henry about repatriating Haitian migrants on the U.S. southern border, the State Department said in a statement.

The two men “discussed the dangers of irregular migration, which puts individuals at great risk and often requires migrants and their families to incur crippling debt,” said State Department spokesman Ned Price.

Blinken said on Twitter that he also spoke to Mexican Foreign Minister Marcelo Ebrard “about our efforts to promote safe, orderly, and humane migration”. Washington has in recent years pressured Mexico into blocking the flow of migrants toward the U.S. border.

U.S. officials closed the Del Rio border crossing last Friday due to the crush of migrants, and said Monday it remained shuttered, with most traffic re-routed to the Eagle Pass, Texas, border crossing, some 55 miles south.

The prospect of deportations weighed heavily on the camp’s residents, some of whom traversed continents over months to reach the border.

“They can’t send us back to Haiti because everyone knows what Haiti is like right now,” said Haitian migrant Wildly Jeanmary late on Sunday, wearing only boxer shorts and standing on the Mexican side of the river after crossing it.

Drenched, he cited July’s presidential assassination as a reason not to return with his wife and their 2-year-old daughter to the poorest country in the Americas. Haiti was also hit by a major earthquake last month.

“The government of the United States has no conscience,” said Nerlin Clerge, another Haitian migrant who stood near the riverbank and had traveled to the camp with his wife and their two young sons. He said he is now considering applying for the right to stay in Mexico.

Mayorkas said he expects between one to three daily repatriation flights back to Haiti, adding that a surge of 600 border agents and other personnel have been deployed to the area.

“If you come to the United States illegally, you will be returned. Your journey will not succeed,” he said at a news conference.

While President Joe Biden rolled back many of his predecessor Donald Trump’s hardline immigration policies earlier this year, he left in place a sweeping pandemic-era expulsion policy under which most migrants caught crossing the U.S.-Mexico border are quickly turned back.