The attack in part of the tribal badlands near the Afghan border was beaten off when troops responded with artillery and heavy weapons, a senior paramilitary Frontier Corps (FC) official told AFP.
The area is cut off to journalists and aid workers and it was not possible to confirm the death toll independently.
“More than 20 militants attacked a Frontier Corps checkpost in Khapiyanga area of Lower Kurram tribal region on Sunday night, which triggered a firefight, killing two soldiers and four rebels,” the FC spokesman said.
“Four troops were also injured in the clash which continued for around 40 minutes.”
“The militants came by foot from the nearby mountains,” the official said on the condition of anonymity.
“When the troops responded, they ran away with four dead bodies of their colleagues. We don’t know how many of the militants got injured.”
Kurram is one of seven districts in Pakistan’s semi-autonomous tribal belt, where Taliban and al Qaeda-linked militants have carved out strongholds used to plot attacks on Pakistani, Afghan and Western targets.