Port-au-Prince (AFP) - The US special envoy to Haiti resigned Thursday two months after his appointment, denouncing the Biden administration's deportation of Haitian migrants from the US-Mexico border back to their poverty-stricken homeland. 

The shock resignation came as tensions built up after Mexican police showed up in force at a Haitian migrant camp in Ciudad Acuna, where thousands of migrants are stuck, unable to cross into the United States.

In Washington, President Joe Biden's administration remained on the defensive, as tens of thousands more people from Haiti and elsewhere who were traveling to the United States massed in Colombia and in Tapachula on Mexico's southern border.

"I will not be associated with the United States inhumane, counterproductive decision to deport thousands of Haitian refugees and illegal immigrants to Haiti," State Department envoy Daniel Foote said in a scathing letter of resignation.

Foote described Haiti as a place where US diplomats "are confined to secure compounds because of the danger posed by armed gangs in control of daily life."

"Mired in poverty, hostage to the terror," Foote wrote, the Haitian population "simply cannot support the forced infusion of thousands of returned migrants lacking food, shelter, and money without additional, avoidable human tragedy."

"More refugees will fuel further desperation and crime," he wrote.

Deportation fears

The resignation came after the Biden administration had already flown 1,400 Haitians back to Haiti on 12 flights.

Many if not most of them had been living in South America for years before making the trek to the US border, hoping to gain asylum.

Unicef said two-thirds of those flown back were women and children.

"When children and families are sent back without adequate protection, they find themselves even more vulnerable to violence, poverty and displacement -- factors that drove them to migrate in the first place," the group said.

Six more flights were expected to land Thursday in Port-au-Prince and Cap-Haitien, according to an official with the International Organization for Migration.

The crisis has built since some 15,000 migrants, the largest part of them Haitian, flowed into Del Rio, Texas from Ciudad Acuna, Mexico in recent weeks.

Footage of the migrants, many of them families, massing under a highway bridge and moving back and forth to Mexico for food, have stunned America and sparked a fresh crisis over migrant policy.

Many Haitian migrants are still in Ciudad Acuna, where they also risk being deported.

On Thursday scores of Mexican police officers arrived at their camp, ratcheting up tensions.

"I have nothing in my country. What am I going to do?" said a Haitian woman who gave her name as Sonia.

'Ignored and dismissed' -

Foote condemned the repatriations in his resignation letter and said the Biden administration was not supporting a return to democracy in Haiti after the July 7 assassination of president Jovenel Moise.

He complained that the  administration "ignored and dismissed" his policy recommendations.

Deputy Secretary of State Wendy Sherman, in an interview with the McClatchy news group, called that charge "false."

But she said some of his proposals would have been "harmful." 

"One of the ideas that Mr. Foote had was to send US military back to Haiti," she said.

"I can tell you that sending US military into Haiti is not the answer that will solve the terrible situation that the Haitian people are currently facing," she said.

Horse patrols ended

The administration continued to struggle to find a solution to the migrants who have already crossed the border.

On Wednesday Homeland Security Secretary Alejandro Mayorkas said he was in talks with Brazil, Chile and other South American countries to send the migrants back to them.

Also on Thursday, the Homeland Security Department said it had halted the use of mounted Border Patrol officers in Del Rio after AFP photographs and other media video footage showed the horsemen appearing to use their mounts and reins to menace Haitian migrants. 

"We have ceased the use of the horse patrol in Del Rio temporarily," a spokesperson said.

"We'll prioritize other methods for identifying individuals who might be in medical distress."

Mayorkas said that the images of the mounted officers "do not reflect who we are as a country, nor do they reflect who the United States Customs and Border Protection is."