Texas Gov. Greg Abbott (R) has sent a fleet of state-owned vehicles to line up for miles as a barricade along the border with Mexico, insisting the state was taking “unprecedented steps,” as thousands of migrants still seek to cross into the United States.

The “steel wall” of cars, as Abbott called it, is only the latest of the stark images coming from the crisis unfolding in Del Rio, Tex., where nearly 15,000 border crossers, many Haitians living in Chile and other South American nations, have arrived.

Migrants trying to cross the Rio Grande from Ciudad Acuña, Mexico into Texas on Sept. 19 were delayed by U.S. border officials on horseback. (Reuters)

The Homeland Security Department is investigating reports that Border Patrol agents on horseback attempted to grab migrants and push them back toward Mexico, captured in scenes Sunday along the Rio Grande.

“What we did, we put hundreds of Texas Department of Public Safety cars and created a steel wall — a steel wall of DPS vehicles — that prevented anybody from crossing that dam that you’ve seen people walk across,” Abbott told Fox News in an interview Tuesday. “We effectively … regained control of the border.”

Abbott has long championed the construction of a physical border wall in Texas, a major priority of President Donald Trump, in addition to the use of “strategic fencing.”

He slammed the Biden administration while insisting his state would continue to take action, including by injecting $2 billion toward border security funding. “It has been the state of Texas that has had to step up,” Abbott said Tuesday at a news conference from Del Rio. “Failure to enforce laws that exist in the United States leads to chaos and chaos leads to inhumanity.”

The Trump administration completed more than 450 miles of 18- to 30-foot steel-bollard fencing topped with anti-climbing plates along stretches of the international boundary, but plans were widely criticized as xenophobic, expensive and having little impact on the crisis.

President Biden, meanwhile, has taken steps to move away from investing in the physical U.S.-Mexico border wall. On his first day in office, he halted construction of the wall and directed his administration to study possibilities for repurposing the project’s funding. However, he has signaled that enforcing the border using technology and personnel remains a priority.

The latest crisis at the border has marked a new inflection point for the Biden administration’s struggles with immigration policy.

As Biden confronts external attacks from Abbott and other Republicans portraying his policies as weak and ineffective, many immigrant rights activists have said that Biden has not lived up to his campaign vows to defend vulnerable foreigners seeking a better life in the United States.

Biden recently also caused an uproar in his party when he balked at increasing the annual cap on refugees before eventually agreeing to do so, after growing backlash from angry Democrats.

During this latest immigration flash point, White House officials on Tuesday struggled to explain the searing images of border agents treating Haitian migrants harshly and attempting to force them back across the Rio Grande into Mexico.

“What I saw depicted about those individuals on horseback treating human beings the way they were, was horrible,” said Vice President Harris, whom Biden tasked with taking the lead on migration issues. “I’m deeply troubled about it,” she added, voicing support for the DHS investigation promised Monday.

Homeland Security Secretary Alejandro Mayorkas also said Tuesday that the activities of the agents had been curtailed while investigations were underway.

“The individuals who are the subject of the investigation are on administrative duties currently,” Mayorkas tweeted. “They are not executing their other law enforcement duties, and they are not to be interacting with other migrants.”

The Biden administration is preparing to nearly double the number of Haitians being deported to Haiti from Texas starting Wednesday, it said, using an emergency provision of the U.S. public health code known as Title 42, which allows authorities to sidestep the usual immigration proceedings.

However, stories of desperate Haitians sleeping under the border bridge in Del Rio only to be turned back have shocked many.

Scores of Haitians camped in the small Texas border town are returning to a shattered country, grappling with the aftermath of a presidential assassination, a deadly earthquake, worsening food insecurity and rising social anarchy amid a grab for territory by gang warlords.

Several deportees — including one who arrived Monday and five others who arrived Tuesday — told The Washington Post they and “many” other deportees had been shackled during transit, including on flights, with one describing it as being chained “like a slave.”

Secretary of State Antony Blinken said Monday he had spoken with Haiti’s Prime Minister Ariel Henry to discuss the “safe repatriation of Haitian migrants on the Southern border,” along with the “grave risks” posed by what he called irregular migration.

Estimates over the weekend from officials said the makeshift camp under the bridge held more than 14,000 people. During Abbott’s visit on Tuesday he said the most recent tally at the camp was about 8,600 migrants.