The fighting began after militants attacked security forces around midnight in Kani Guram, a mountainous area about 30 miles northeast of Wana, the main town in South Waziristan, said army spokesman Brig. Shahjehan Ali Khan.
Khan said that based on reports from the scene, six militants were killed but the bodies hadn't been retrieved yet and it wasn't known whether they were foreigners or local tribesmen. Both sides were using mortars, rockets and small arms, Khan said.
Residents reported hearing artillery and gunfire since dawn in another area near Kani Guram.
In recent days, an offensive by army and paramilitary troops in South Waziristan has left about 60 fighters dead, many of them Uzbeks, Chechens and some Arabs.
On Thursday, the army said fighter jets and helicopter gunships smashed an alleged Al Qaeda-linked terrorist training facility northeast of Wana. Ten other suspected militants were killed in another location on the same day.
The army said Friday it also captured five foreigners trying to flee the area — but did not disclose their identities or nationalities — and seized several computers, dozens of CDs and some unspecified written material.
Khan denied a newspaper report Sunday that civilians were killed in the raid on the training camp. The Dawn daily said that half the dead were local people and included some students.
Hundreds of foreign fighters are believed to be hiding in South Waziristan, where Usama bin Laden (search) and his top lieutenant Ayman al-Zawahri (search) are also suspected to shelter although there is no hard evidence of that.