At least 12 Afghan soldiers were killed while asleep in their outpost by two soldiers of their own battalion, an official said on Tuesday.
The incident occurred just after midnight on the outskirts of Kunduz. The city was briefly captured by the Taliban last year in a blow to Afghan forces, the first time the group seized a provincial capital since losing power in 2001.
Insider attacks have plagued both Afghan and international military forces in the country, undermining trust and morale.
Attacks on foreign forces have made international headlines in the past. Analysts, however, complain lax hiring policy and the plight of Afghan soldiers goes largely unnoticed. Economic disparity between foreign and local forces in Afghanistan, they say, makes it easier for increasing discontent among the Afghan National Security Forces ranks.
Links with Taliban
Afghan authorities claim the two soldiers are suspected to have links with the Taliban and that the killing was a so-called "insider attack".
"The two soldiers fled after killing 12 sleeping colleagues in Zakhil Khoman area of Kunduz," senior local police commander Sher Aziz Kamawal said.
"We have launched an investigation into the incident."
AFP quoted Mahmood Danish, the Kunduz governor's spokesperson, as giving a higher death toll of 13 and said the "rogue" soldiers prepared the way for the Taliban to storm their checkpoint and carry out the killings.
Authorities estimate about 5,000 local police and troops were killed in 2015, with an additional 15,000 wounded.