Three American troops were killed in an insurgent attack in eastern Afghanistan on Friday, a senior defense official said.
Details of the attack were not released.
NATO said another one of its troops died in a roadside bomb explosion in the south. It did not release further details or the nationality.
The deaths raise the number of international troops killed in September to 11. A total of 334 members of the international military coalition have died so far this year.
More than 1,760 American troops have died serving in the war in Afghanistan, which is approaching the end of its 10th year.