Two U.S. troops were killed in Afghanistan on Wednesday in a helicopter crash, military officials have announced.

While the cause of the crash is under investigation, there are no preliminary indications that the helicopter was downed by enemy fire, according to a U.S. Forces Afghanistan news release.

No further information about the crash was immediately available.

The names of both of the service members killed are being withheld pending next of kin notification.

A total of 22 U.S. troops have been killed supporting operations so far in 2019. Two other veterans have been killed in Afghanistan this year while working as defense contractors.