A U.S. service member was killed and another was wounded Monday during an attack against NATO forces in Afghanistan, according to the military command there.

Officials from Operation Resolute Support said the unnamed American was killed during an "apparent insider attack in eastern Afghanistan."

“The sacrifice of our service member, who volunteered for a mission to Afghanistan to protect his country, is a tragic loss for all who knew and all who will now never know him,” said Gen. Scott Miller, head of U.S. Forces-Afghanistan. “Our duty now is to honor him, care for his family and continue our mission.”

Officials did not disclose the names of the deceased or injured, but said the identities will be shared with the public 24 hours after the members' families are notified of the incident.

The deceased service member is the sixth American to be killed while serving in Afghanistan in 2018.

Operation Resolute Support involves more than 13,000 troops and began in January 2015.