KABUL, Afghanistan — The U.S.-led international military coalition says four of its service members have been killed in southern Afghanistan and a military official confirms all were Americans killed by an improvised explosive device.

NATO said in a statement that the four were killed Sunday during a partnered operation in the south, but did not provide any further details or their nationalities.

A military official confirmed the four were from the United States and were killed by an IED. The official spoke on condition of anonymity because the official was not authorized to speak publicly.

No other details were available.

IED's have become one of the top killers of Afghan and foreign soldiers, as well as civilians.