Kabul, Afghanistan (CNN) -- Five of the nine U.S. military members killed in a helicopter crash in southern Afghanistan this week were from the 101st Combat Aviation Brigade based at Fort Campbell, Kentucky, according to a statement from the base Wednesday.
Families of the five soldiers have been notified, but the names have not yet been released by the military, the statement said.
The crash occurred Tuesday in the Daychopan district of Zabul province, one of several turbulent southern regions where coalition and Afghan troops have been battling the tenacious militant group for years. The cause of the crash remains unknown.
"There are no reports of enemy fire at the time the aircraft went down," NATO's International Security Assistance Force told CNN on Tuesday.
Along with the nine U.S. military members killed, two other service members, as well as an Afghan National Army soldier and an American civilian, were injured in the crash. They were taken to a NATO medical facility.
In the first public acknowledgement of U.S. troop involvement in the deadly crash, Pentagon spokesman Col. Dave Lapan confirmed earlier Wednesday that nine U.S. service members were killed in the incident.
A CNN tally brings the number of coalition troop fatalities so far this year to 526, including 350 Americans, surpassing the previous highs -- 516 coalition troop deaths, including 313 Americans -- in 2009.
CNN Pentagon producer Larry Shaughnessy contributed to this report.