A member of the Nato-led forces has been shot dead by a man in Afghan army uniform, military officials say.
The assailant was also killed during the attack, which took place in southern Afghanistan, they added.
This year has seen a sharp rise in so-called insider attacks against local forces and Nato troops in Afghanistan.
The attack came hours before President Karzai was due in the US for a visit seen as key to the future of the American presence in Afghanistan.
An investigation is under way to determine if the attacker had links to insurgents, the International Security Assistance Force (Isaf) said in a statement on Tuesday.
Military commanders refer to such rogue attacks as “green-on-blue” – green for Afghan forces and blue for the Nato coalition.
President Hamid Karzai is expected to arrive in the US on Tuesday for a three-day visit, which will include a meeting with Mr Obama on Friday.
Nato forces are committed to training Afghan security forces before foreign combat troops pull out by the end of 2014.
–BBC
