The coalition recently shifted its focus from southern Afghanistan to the east, where militants are fighting Afghan and coalition troops along the long, porous border with Pakistan.
The exact location of the bombing was not disclosed, nor were the nationalities of the dead.
So far this year, 519 NATO service members have been killed in Afghanistan, including at least 389 Americans.
Separately, tribal elders in Logar province, also in the east, continued to negotiate with insurgents on Saturday in an effort to free eight Pakistani laborers kidnapped by militants on Thursday, said provincial spokesman Din Mohammad Darwesh.
He said they were kidnapped by a gunman on a motorcycle who ambushed a bus carrying the laborers to work at a hospital construction site in Pul-e-Alam, the provincial capital. The assailants took them into the woods at gunpoint.