"Two International Security Assistance Force-contracted civilians died as the result of a vehicle-borne improvised explosive device attack in eastern Afghanistan today," the statement said.
Haroon Zarghun, a spokesman for the militant Hezb-e-Islami, said the Taliban-aligned group took credit for the attack, saying it was carried out by a "martyrdom seeker" targeting a U.S. convoy, the Wall Street Journal reported.
"He has been watching them since a week and was looking for an opportunity to target the convoy and not harm civilians," Zarghun said. "We only carry martyrdom-seeking attacks on foreigners. We don't conduct such attacks against Afghan police, army and civilians."
The blast damaged a vehicle in the convoy, a civilian's car and blew out windows of houses, officials said.
In keeping with its policy, the ISAF said it deferred casualty identification procedures to the appropriate national authorities.