(Kabul)  --  Six American soldiers are dead following an aircraft crash in southern Afghanistan.  The Taliban claimed responsibility for the crash on Twitter, saying its fighters shot down a helicopter that was "flying at low altitude" in Zabul province.  The crash is the single most deadly incident to hit NATO this year.  NATO says in a statement that the crash is under investigation.  

The most deadly incident of this type took place in August of 2011, when the Taliban shot down a transport helicopter.  All 38 people on board were killed, including 25 U.S. Special Ops forces.