Col. Wayne Shanks says the deaths occurred Tuesday. He did not release any other details when he spoke Wednesday.
Violence has risen across Afghanistan in the last three years as the resurgent Taliban have regained control of large swaths of countryside.
Fighting has been particularly harsh this summer in the south, where thousands of U.S. troops have been deployed to bolster the Canadian and British-led operations in the Taliban heartland.
This year has been the deadliest for U.S. and NATO troops since the 2001 invasion.