CIUDAD ACUNA, MEXICO -- Haitian migrants milled around makeshift shelters held up with giant reeds, as wind blew dust through the camp littered with plastic bottles and overflowing trash bags. Some migrants sat on plastic paint cans or the ground while others hung clothes to dry on the bamboo-like carrizo cane.

All waited to learn their fate at a dramatically diminished Texas border encampment where almost 15,000 migrants had gathered just days ago under a bridge between Del Rio, Texas, and Ciudad Acuna, Mexico.

About 4,000 remained on Thursday, Department of Homeland Security officials said. The number had peaked on Saturday, as migrants driven by confusion over the Biden administration's policies and misinformation on social media converged at the crossing.

But the United States and Mexico appeared eager to end the increasingly politicized humanitarian situation that prompted the resignation of the U.S. special envoy to Haiti and fresh condemnation from civil rights leader Rev. Al Sharpton and UNICEF.

DHS officials said about 1,400 migrants had been sent to Haiti on 13 flights, rapidly expelled under the pandemic public health authority known as Title 42. Another 3,200 were in U.S. custody and being processed, while several thousand have returned to Mexico, DHS officials said, speaking on condition of anonymity to brief journalists about an ongoing operation.

Mexico's immigration agency had estimated late Wednesday there were as many as 600 migrants in Ciudad Acuna. The riverside camp appeared to hold that many at its peak, while other migrants were scattered through the city in hotels and private homes. A city official said Wednesday that Mexican authorities had removed about 250 Haitian migrants from the city since Sunday evening. Still, "several thousand" migrants returning to Mexico from the Del Rio camp seemed an exaggeration.

Haitians camped in Mexico awoke Thursday surrounded by security forces, with a helicopter thundering overhead and state police trucks spaced every 30 feet or so between their tents and the water's edge.

After anxious minutes of indecision, dozens of families hurried into the river to cross at a point where there was only one municipal police vehicle, calculating it was better to take their chances with U.S. authorities.

Guileme Paterson, a 36-year-old from Haiti, appeared dazed. "It is a difficult moment," she said before beginning to cross the Rio Grande with her husband and their four children.

"Things are going badly," said Michou Petion, carrying her 2-year-old son in her arms toward the river. Her husband carried bags of belongings and several pairs of sneakers dangled around his neck.

"The U.S. is deporting a lot to Haiti, now I don't know if I can enter or leave," Petion said.

Texas Department of Public Safety officials allowed journalists to visit the camp later Thursday but prevented them from talking to migrants. For those who remained, food, shelter and medical care was being provided to those who need it, U.S. officials said.

At one point, two men riding in an ATV emblazoned with "Homeland Security" approached a group of women holding infants and said in Spanish: "We have food for the baby." The women approached the men, who handed them a small container.

A low dam that had been used to cross from Mexico into the U.S. was closed, and a worker picked up mounds of discarded belongings that included cell phone chargers, clothing and Styrofoam containers.

Sharpton said Thursday that he toured the camp and witnessed "a real catastrophic and human disgrace." A handful of protesters, some wearing camouflage hats from former President Donald Trump's 2020 campaign, shouted through the entirety of Sharpton's remarks.

"Del Rio is not a racist city. Del Rio is a loving, caring community," one protester yelled while Sharpton spoke to reporters.

Sharpton vowed to "continue to come back ... and stand with our people and make sure asylum is treated in one way and one manner."

Some Haitians are being allowed to remain in the U.S. at least temporarily to seek asylum or to stay under some other claim to residency, with notices to appear later before immigration authorities. DHS officials declined to specify the number but said they are people with particular "vulnerabilities," which can mean they have young children or are pregnant, or because the U.S. doesn't have capacity to hold them in detention, especially during the pandemic.

There are no plans to stop expelling other migrants under Title 42, despite pressure from Democratic lawmakers, who say migrants are being sent back to a troubled country that some left more than a decade ago.

The provision was put in place by the Trump administration in March 2020 to justify restrictive immigration policies in an effort to prevent the spread of the coronavirus. But the Biden administration has used Title 42 to justify the deportation of Haitian migrants.

A federal judge late last week ruled the regulation was improper and gave the government two weeks to halt its use, but the Biden administration on Monday appealed the decision.

Officials said Thursday that the U.S. State Department also is in talks with Brazil and Chile to allow some Haitians who previously resided in those countries to return, but the issue is complicated because some no longer have legal status there.

Meanwhile, the U.S. special envoy to Haiti, Daniel Foote, submitted a letter of resignation protesting the "inhumane" large-scale expulsions of Haitian migrants.

Foote, who was appointed only in July, wrote Secretary of State Antony Blinken that he was stepping down immediately "with deep disappointment and apologies to those seeking crucial changes."

"I will not be associated with the United States inhumane, counterproductive decision to deport thousands of Haitian refugees and illegal immigrants to Haiti, a country where American officials are confined to secure compounds because of the danger posed by armed gangs to daily life," he wrote. "Our policy approach to Haiti remains deeply flawed, and my policy recommendations have been ignored and dismissed, when not edited to project a narrative different from my own."

The career diplomat was known to be deeply frustrated with what he considered a lack of urgency in Washington and a glacial pace on efforts to improve conditions in Haiti.

State Department spokesman Ned Price disputed Foote's assertions, saying his proposals had been "fully considered in a rigorous and transparent policy process."

"Some of those proposals were determined to be harmful to our commitment to the promotion of democracy in Haiti and were rejected during the policy process. For him to say his proposals were ignored is simply false," Price said.

UNICEF also condemned the expulsions, saying initial estimates show more than two out of three migrants expelled to Haiti are women and children, including newborns, and about 40% in Del Rio are children.

"Haiti is reeling from the triple tragedy of natural disasters, gang violence and the COVID-19 pandemic," said Henrietta Fore, UNICEF's executive director, who said those sent back without adequate protection "find themselves even more vulnerable to violence, poverty and displacement -- factors that drove them to migrate in the first place."

DHS officials said about two-thirds of those under the bridge are families and the rest are single adults.

But even as the number of Haitian migrants gathered in Del Rio dwindled, a few groups of Cubans were seen walking along a dirt road toward the camp at the bridge on Thursday.

As a group of three men approached, a DPS officer yelled out, "We got migrants!" One of the men said in Spanish: "We're here. We made it to the country of liberty."

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Lozano reported from Del Rio, Texas. AP journalists Julio Cortez in Del Rio, Texas, Joshua Goodman in Miami, Matthew Lee in New York, Danica Coto in San Juan, Puerto Rico, and Tammy Webber in Fenton, Michigan, contributed to this story.