WASHINGTON, D.C. – Defense Department officials said April 20 the four International Security Assistance Force members killed in a helicopter crash in southern Afghanistan yesterday were Americans.

“Regrettably, we can confirm that four U.S. service members lost their lives in this crash,” George Little, acting assistant secretary of defense for public affairs, told Pentagon reporters today.

Pentagon spokesman Navy Capt. John Kirby, who returned this week from approximately two months’ duty in Afghanistan, said no information is yet available on the mission the helicopter crew was performing.

“We still believe that weather was the principal cause [of the accident],” Kirby said.

He added that as with all such incidents, the crash remains under investigation until all possible details are determined.

“They’re going to look at all factors, but right now it appears that weather was the principal cause,” Kirby said.

He said defense officials are not aware of any enemy fire reported in the area where the crash took place.