A helicopter operated by the NATO-led International Security Assistance Force crashed in southern Afghanistan, dpa cited the alliance as announcing. All four on board were believed dead, according to a news report. The Black Hawk aircraft came down in bad weather Thursday while attempting to pick up a group of soldiers, a US military spokesman was quoted as saying by CNN. The four US personnel on board were presumed killed, the spokesman said. Enemy action had not been ruled out as a cause for the crash, he was reported as saying. The ISAF confirmed the incident and said the crash site had been secured. It did not release any further information about the crash or the fate of those on board.