Maj. Lori Hodge, an International Assistance Security Force spokeswoman, said the uniformed assailant fired on troops in restive Helmand province, killing three, but provided few details, CNN reported.
In the other incident, insurgents killed the NATO soldier, officials said.
The latest reported killings occurred a day after U.S. Secretary of State Hillary Clinton condemned an attack Wednesday in eastern Kunar province in which a U.S. foreign service officer, three coalition troops and an Afghan civilian died. Several others were injured.
The Taliban claimed responsibility for the Kunar province attack.