US secretary of Homeland Security Alejandro Mayorkas defended his department on September 22 after images showing horse-mounted immigration officers chasing down Haitian migrants on the border with Mexico went viral.

Pictures by AFP photographer Paul Ratje on September 20 that were published repeatedly in media across the US and around the world showed border patrol riders appearing to swing their mounts’ long reins to threaten undocumented migrants and push them back to the Rio Bravo river – known in the US as the Rio Grande – that marks the Mexico-US frontier.

The images “do not reflect who we are as a country, nor do they reflect who the United States Customs and Border Protection is”, Mayorkas told the House Homeland Security Committee.

“I have ordered an investigation to be conducted of the events that are captured in those images,” he said.

“The facts will drive the actions that we take, we ourselves will pull no punches,” he said, promising a result “in days and not weeks”.

Critics said the images from Del Rio city, Texas state were reminiscent of both cowboys attempting to herd livestock and times in history when horse-mounted police, prison guards or slave owners used whips against Black Americans.

They came as Mayorkas’ department struggles to halt thousands of Haitians and people from other countries crossing Mexico’s northern border hoping to stay in the US.

The Border Patrol began deporting the Haitians back to their country by air over the weekend.

But after the images of the horsemen and the migrants spread, members of President Joe Biden’s Democratic Party condemned the treatment.

“I urge President Biden … to immediately put a stop to these expulsions,” said US Senate leader Chuck Schumer.

As migrants continued to cross the border on September 22 and thousands remained camped under a bridge in Del Rio, Mayorkas said his department was working to deter arrivals.

“We do have a plan to address migration at the southern border, we’re executing it. It takes time and we’re starting to see the results,” he told the panel.

Many of the Haitians have migrated from countries in South America where they fled to years earlier, especially following the massive 2010 earthquake that devastated the Caribbean country.

In Colombia on September 22, a government official said 19,000 migrants, mainly Haitians, were amassed on that country’s north coast, hoping to cross to Panama and find a route to the US.

As the US government has been putting Haitians on aircraft to send back to Haiti, Mayorkas said he was in discussions to send some back to South America as well.

“We are working with countries in South America – Chile and Brazil, for example – to see whether they would accept the return of Haitians who’ve travelled from those countries,” Mayorkas said, calling the issue “complicated”.

Meanwhile the senior Republican in Congress, Senator Mitch McConnell, blamed the Biden administration and “left-wing” Democrats for encouraging the migrants to come.

“They say their approach to immigration is the compassionate path, the one that reflects the soul of America,” McConnell said of the Democrats.

“They are wrong. No way does it honour the American soul or uphold American values to tolerate a major border security crisis,” he said.