The number of migrants detained after entering the US across the southern border fell 28 percent in June from May as both the United States and Mexico tightened controls, the Department of Homeland Security announced Tuesday. DHS credited its "whole of government approach" for the decline, after apprehensions rocketed above 144,000 in May, overwhelming the government's capacity for housing the migrants and exacerbating the squalid conditions in holding cells for new arrivals. While migrant flows usually ebb in the hot summer, DHS said initiatives with El Salvador, Guatemala and Honduras, the sources of most of the migrants, and a joint crackdown with Mexico, whose territory most of them must transit, had contributed to the downturn.