CIUDAD ACUÑA, Mexico — Mexico has begun busing and flying Haitian migrants away from the U.S. border, authorities said Tuesday, signaling a new level of support for the United States as a giant refugee camp in a small Texas border town presented President Biden with a humanitarian and increasingly political challenge.

Mexico has helped at key moments before. It intensified patrols to stop unaccompanied Central American children from reaching the Texas border in 2014, allowed tens of thousands of asylum-seekers to wait in Mexico for hearings in U.S. immigration courts in 2019 and, just last month, began deporting Central American migrants to Guatemala after the Biden administration flew them to southern Mexico.

Marcelo Ebrard, Mexico’s foreign relations secretary, said Tuesday he had spoken with his U.S. counterpart, Secretary of State Antony Blinken, about the Haitians’ situation. Ebrard said most of the Haitians already had refugee status in Chile or Brazil and weren’t seeking it in Mexico.

“What they are asking for is to be allowed to pass freely through Mexico to the United States,” Ebrard said.

Two Mexican federal officials, who requested anonymity because they were not authorized to speak publicly, confirmed Mexico’s actions.

One of the officials said three busloads of migrants left Acuña on Tuesday morning for Piedras Negras, about 55 miles down the border, where they boarded a flight to the southern city of Villahermosa in the state of Tabasco.

The other official said there was a flight Monday from the northern city of Monterrey to the southern city of Tapachula near the Guatemala border. Tapachula is home to the largest immigrant detention center in Latin America. The flight carried about 100 migrants who had been picked up around the bus station in Monterrey, a hub for various routes north to the U.S. border.

The second official said the plan was to move to Tapachula all Haitians who had already solicited asylum in Mexico, since Tapachula is where most of them would have applied and they can only legally remain in Mexico while their case is processed if they stay in the south.

The Haitian migrants who are already in Mexico’s detention centers and have not requested asylum will be the first to be flown directly to Haiti once Mexico begins those flights, according to the official.

Dozens of migrants upset about being deported to Haiti tried to rush back into a plane that landed Tuesday afternoon in Port-au-Prince as they yelled at authorities. A security guard closed the plane door in time as some deportees began throwing rocks and shoes at the plane. Several of them lost their belongings in the scuffle as police arrived. The group was disembarking from one of three flights scheduled for the day.

Republican Texas Gov. Greg Abbott, during a visit Tuesday to an encampment in Del Rio, Texas, said the county’s top official told him the most recent tally was about 8,600 migrants who remain there. He continued to slam the Biden administration and expressed skepticism the area would be cleared soon.

“They have shown no capability of being able to process all of these migrants by the end of the week,” Abbott said. “The only thing they have shown is an incapability of dealing with this crisis, candidly in a way where they pretend it doesn’t even exist. We’re here to tell you, it exists, it’s total chaos, and the Biden administration, they need to up their game big time.”

About six dozen officers with the U.S. Bureau of Prisons were in place Tuesday near Del Rio, according to three people familiar with the matter. The officers are mainly assisting U.S. Customs and Border Protection with transporting the migrants on Bureau of Prisons buses between detention facilities and from the Del Rio bridge, the people said. The people could not discuss the matter publicly and spoke to the AP on condition of anonymity.

The rapid expulsions were made possible by a pandemic-related authority adopted by former President Donald Trump in March 2020 that allows for migrants to be immediately removed from the country without an opportunity to seek asylum. President Biden exempted unaccompanied children from the order but let the rest stand.

Any Haitians not expelled are subject to immigration laws, which include rights to seek asylum and other forms of humanitarian protection. Families are quickly released in the U.S. because the government cannot generally hold children.

Haitians have been migrating to the U.S. in large numbers from South America for several years, many having left their Caribbean nation after a devastating 2010 earthquake. After jobs dried up from the 2016 Summer Olympics in Rio de Janeiro, many made the dangerous trek by foot, bus and car to the U.S. border, including through the infamous Darien Gap, a Panamanian jungle.

Some of the migrants at the Del Rio camp said the recent devastating earthquake in Haiti and the assassination of President Jovenel Moïse make them afraid to return to a country that seems more unstable than when they left.

“It’s not right,” said Haitian migrant Jean Philipe Samus. “The Americans are grabbing Haitians and deporting everyone to Haiti. Haiti has no president, no jobs, there is nothing. In the earthquake a lot of people died. It’s not right over there, I’m going back to Mexico.”