He said there were no USA or North Atlantic Treaty Organisation fatalities, but noted that US soldiers were wounded.
Authorities say an Afghan solider attacked and wounded US soldiers at a military base on Saturday.
The injured troops have been evacuated for treatment, the mission said in a statement.
"Initial information shows three USA soldiers visiting the base were wounded", ministry spokesman Mohammad Radmanish told AFP, adding that the attacker had been gunned down.
North Atlantic Treaty Organisation said an investigation into the incident has been launched.
The shootout at Camp Shaheen near northern Mazar-i-Sharif city is the second "green-on-blue" attack - where Afghan soldiers turn their weapons on worldwide forces assisting them - reported this week.
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Militants plan so-called green-on-blue attacks in order to destabilize trust between Western service members and local soldiers, but they can also stem from local soldiers lashing out due to personal grievances. The U.S. statement did not confirm the nature of the incident or state the exact number of casualties.
"US soldiers have been wounded". The gunman - an Afghan - had been shot and killed, the spokesman said.
A Taliban spokesman praised the attack but did not claim responsibility.
No US troops were killed.
The attackers, some dressed in Afghan military uniforms, managed to pass through two checkpoints in military vehicles before being stopped, after which they opened fire on the busy compound.