Pakistani army helicopter gunships began attacking a suspected hideout in the North Waziristan tribal region late on Thursday following a clash.
Military spokesman Major-General Shaukat Sultan said several other Pakistani soldiers had been wounded. The fighters were also believed to have suffered heavy casualties, he said.
"There was heavy resistance from the other side," Sultan said.
Pakistan has been trying to clear its lawless tribal areas on the Afghan border of armed men for the past two years. Hundreds of fighters and Pakistani soldiers have been killed in clashes.
Many al-Qaida members and their Taliban allies were believed to have slipped into Pakistan after US led forces ousted the Taliban government in Afghanistan in the wake of the 9/11 attacks on the United States.
Sultan, commenting on speculation a rebel leader might be holding out in the North Waziristan region, said the military had no evidence of any leader there.
"Certainly, there were reports about militants but there were no reports of any high-value target"
Major-General Shaukat Sultan, Pakistan military spokesman
"Certainly, there were reports about militants but there were no reports of any high-value target," he said.
The fighting was continuing at dusk on Friday, he said. North Waziristan is about 400km southwest of the capital, Islamabad.
On Thursday, a soldier was killed and three seriously wounded when armed men opened fire on a convoy in the region, while in South Waziristan, four soldiers and a government official were killed in a similar ambush.
A security official on the border said troops had arrested a nephew of a Taliban leader, Jalaluddin Haqqani, during a search in North Waziristan this week.
Haqqani had set up an Islamic school on the outskirts of the main town in North Waziristan, Miranshah, years ago.
Haqqani's whereabouts were not known but the official said his school was serving as a rebel nerve centre.