A NATO soldier was killed when an apparent insider attack sparked a firefight between US and Afghan troops in the east of the country on Wednesday, officials said.
The gunfight erupted after an Afghan soldier opened fire on an American delegation outside the governor's compound in Jalalabad, the capital of the militant-infested province of Nangarhar.
"US soldiers returned fire, killing the shooter and wounding two other members of the Afghan National Army. We are investigating to find out the motive behind the shooting," Nangarhar police chief Fazel Ahmad Shirzad told AFP.
A NATO soldier was also killed.
The "incident in Jalalabad today resulted in the death of one Resolute Support service member", said a brief statement from Resolute Support, the new name for the NATO mission in Afghanistan.
It did not give the natinality of the victim.
Monica Cummings, the US embassy spokeswoman, said the incident occurred after a senior US official held a meeting with the provincial governor in Jalalabad.
So-called "green-on-blue" attacks -- when Afghan soldiers or police turn their guns on international troops -- were a major problem during NATO's long years fighting alongside Afghan forces.
But the rate of such incidents has dropped sharply in recent years.
Three American contractors were killed in an apparent "insider attack" at Kabul airport in January.
NATO troops have adopted special security measures in recent years to try to counter the threat.
President Barack Obama last month reversed plans to shrink the US force in Afghanistan this year by nearly half, an overture to the country's new reform-minded leader, President Ashraf Ghani.
Hosting Ghani at the White House for their first presidential head-to-head, Obama agreed to keep the current level of 9,800 US troops until the end of 2015.
The Taliban, waging a deadly insurgency since they were ousted from power in late 2001, warned that the announcement would damage any prospects of peace talks as they vowed to continue fighting.