The decision to return migrants fleeing an earthquake and political instability was “inhumane”, senior diplomat Daniel Foote said in a damning letter.
Last weekend, the US started deportation flights from a Texas border town where about 13,000 migrants had 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 Cubans, Peruvians, Venezuelans and Nicaraguans are also present.
Since Sunday, the US has returned to Haiti 1,401 migrants from the Texas camp on the border with Mexico.
But in his resignation letter, Mr Foote said Haiti was a “collapsed state” that “simply cannot support the forced infusion of thousands of returned migrants lacking food, shelter, and money without additional, avoidable human tragedy”.
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.
Full article can be view at : https://www.bbc.com/news/world-us-canada-58667660
First published by BBC news.