media captionThousands of people are camped out at the US-Mexico border bridge in poor conditions
The US special envoy for Haiti has resigned in protest over the deportation of Haitian migrants.
The US decision to send the migrants to a country where armed gangs controlled daily life was inhumane, Daniel Foote said in his resignation letter.
Last weekend, the US started flying out migrants from a Texas border town which has seen an influx, with some 13,000 having gathered under a bridge.
They have been waiting in a makeshift camp in temperatures of 37C (99F).
Local officials have struggled to provide them with food and adequate sanitation.
Most of those at the camp are Haitians, but there are also Cubans, Peruvians, Venezuelans and Nicaraguans present.
Since Sunday, the US has returned to Haiti 1,401 migrants from the Texas camp on the border with Mexico. On Wednesday, chaos broke out at Haiti's main airport as flights carrying those being being deported arrived.
But Mr Foote said Haitians "simply cannot support the forced infusion of thousands of returned migrants lacking food, shelter, and money without additional, avoidable human tragedy".
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Shocking images of horse-mounted US officers corralling the migrants have evoked dark comparisons to US slavery and the country's historical mistreatment of black people.
The widely shared images, taken by an AFP photographer earlier this week, appear to show US Border Patrol agents on horseback using their reins against the migrants and pushing them back towards the Rio Grande river that divides Texas and Mexico.
Many Haitians left the country after a devastating earthquake in 2010, and a large number of those in the camp had been living in Brazil or other South American countries and travelled north after being unable to secure jobs or legal status.
This year has brought further hardship for the impoverished country. In July, Haiti's President Jovenel Moïse was assassinated – and in August it suffered another deadly earthquake.
image source, AFPimage captionShocking images of horse-mounted US officers corralling the migrants have been widely criticised