"Two International Security Assistance Force contracted civilians died as the result of a vehicle-borne improvised explosive device attack in eastern Afghanistan today," ISAF said in a statement.
A US official, speaking on condition of anonymity, said the slain contractors were American.
Afghanistan's future remains uncertain as the Taliban continue their insurgent campaign.
NATO forces have already begun to withdraw from Afghanistan, but the United States and other nations have been seeking to keep some troops in Afghanistan after 2014.
On Saturday, the United Nations said that civilian deaths increased in 2013 as fighting intensified between government forces and insurgents.
RA/NJF