BBC News:- Images which appear to show border agents on horseback driving migrants back to a river like cattle have sparked an investigation in the US. The pictures widely shared on social media show the riders using their reins against the migrants and pushing them back towards the Rio Grande in Texas. Homeland Security Secretary Alejandro Mayorkas says his department will investigate reports of alleged abuse. He said the officers were trying to manage the migrants crossing the river. Some 13,000 mainly Haitian migrants have gathered in a makeshift camp under a bridge connecting Del Rio to Mexico's Ciudad Acuña