An attacker wearing an Afghan army uniform shot dead three NATO soldiers in the east of Afghanistan on Saturday, the military coalition said in a statement, dpa reported.
NATO and Afghan officials were "assessing the incident to determine the facts," it added, giving no further details.
General Zahir Azimi, the spokesman for the Afghan Defence Ministry, confirmed the incident which he said took place in Gardez city, the provincial capital of Paktia.
He said it was not immediately clear whether the individual was a Taliban insurgent in disguise or a member of the Afghan army.
Last year more than 60 NATO soldiers and contractors were killed by Afghan security forces in the "green-on-blue" incidents, prompting serious concerns for the coalition.
With more security in place, the number of such attacks and fatalities went down this year.
Elsewhere, a prominent Taliban commander who was the group's shadow governor in a northern Afghan district was killed along with 10 colleagues, Afghanistan's Ministry of Interior said.
"Mohebbullah, also called as Moheb Lang (Moheb the Lame), was killed along with two other insurgent commanders, two suicide bombers and six foreign citizens in a special operation launched by Afghan security forces," the ministry said in a statement.
As shadow governor, he commanded 120 members of the Taliban in Kapisa province's Nejrab district and was suspected of organizing attacks, abductions and youth recruitment, the ministry said.
The statement also said that police arrested another Taliban commander active in Kapisa province, located north-east of Kabul.
Qari Maazullah, who was said to be involved in several terrorist attacks, was arrested by intelligence forces in Pul-e-Charkhi area, the ministry said.