A gunfight broke out between Afghan and foreign soldiers on the outskirts of the capital Kabul on Saturday, killing at least one Afghan serviceman and injuring a number of other soldiers, according to Afghan and NATO officials.
So-called "insider attacks" are severely straining ties between the NATO-led alliance and the Kabul authorities and further undermine waning support for the war in the West.
They have become one of the Taliban insurgents' most effective weapons against the coalition.
"There was an argument between an Afghan and foreign soldier inside a military base… where they opened fire on each other. An investigation is ongoing," defense ministry spokesman Dawlat Waziri said.
The soldier killed was Afghan, a spokesman for the NATO-led force said. A number of others were reported to have been injured.
Insider attacks have been on the rise in recent months, with at least five reported since Sept 21, compared to 11 incidents since the start of the year.
A flurry of attacks last year prompted the coalition to briefly suspend joint military operations, a cornerstone of its mission, and adopt measures limiting interaction between troops.
"If it gets worse it'll make the coalition plan for post-2014 come apart pretty quick," said an army strategist working on those plans.
Most foreign combat troops are due to leave by the end of next year, but a small mission may remain in Afghanistan to continue supporting its newly-formed military and police forces.
Afghanistan and the United States have not yet agreed on several issues in a bilateral security pact and Washington has threatened to pull out its troops next year unless differences are ironed out soon.
Two years ago, the United States ended its military mission in Iraq with a similar "zero option" outcome after the failure of talks with Baghdad authorities.
