The tribal sources further told Aljazeera the clashes, going on for days now, were among the fiercest to date.
The Pakistani army is facing fierce resistance from fighters hiding in the mountains, the sources added.
North Waziristan is about 400km southwest of the capital, Islamabad.
Reuters reported quoting an unidentified official that the deadly clash last on Thursday followed a search by security forces of an area called Hamzoni, about 5km west of the province's main town of Miranshah.
Pakistani security officials told Reuters that army helicopter gunships pounded a suspected fighters' hideout in mountains along the border with Afghanistan on Friday but there was no immediate word on casualties.
Pakistani security forces launched an attack on the suspected hideout in the North Waziristan tribal region late on Thursday following a clash with fighters.
Another security official said troops had arrested a nephew of a Taliban leader, Jalaluddin Haqqani, during a search. Haqqani had set up an Islamic school, or madrasa, on the outskirts of Miranshah years ago.
Haqqani's whereabouts were not known but the official said his school was serving as an extremist nerve centre.