Afghanistan forces were in helicopter crash in southern U.S. . International Security Assistance Force received report that troops came under mortar fire after crash . Officials say no conclusions reached yet in crash initially blamed on mechanical failure . `` We believe there was some sort of enemy engagement once the helicopter crashed , '' one of the officials said . August 2012 's toll worst single-day for U.S. troops since Tuesday .
Afghanistan forces were in helicopter crash in southern U.S. . International Security Assistance Force received report that troops came under mortar fire after crash . Officials say no conclusions reached yet in crash initially blamed on mechanical failure . August 2012 's toll worst single-day for U.S. troops since Tuesday .