The service members were both killed on Monday, Resolute Support said in a statement without providing additional details.
Their names are being withheld for 24 hours after notification of next of kin is complete.
Their deaths come less than a week after a Croatian soldier with the NATO Afghanistan mission was killed and two others seriously wounded in a Taliban suicide attack in Kabul.
On July 13, Sergeant Major James G. Sartor, a U.S. special forces soldier, was killed by small arms fire during operations in Faryad province in northern Afghanistan.
The deaths of the two service members on Monday bring to 12 the number of American forces killed in Afghanistan this year, the same number as all of 2018.