Pakistan's army says eight soldiers ambushed close to the Afghan border have been murdered in cold blood.
More than 35 soldiers have died in the fighting
The army has been engaged in an 11-day offensive against members of al-Qaeda, the Taleban and local tribesmen supporting them.
The soldiers were part of a convoy ambushed on Monday in which it was already reported that 11 other soldiers had been killed.
An army spokesman said the eight men had been shot at point-blank range.
Major General Shaukat Sultan said the killers of the eight soldiers did not deserve any mercy. He called their deaths the worst kind of terrorism.
The army found the eight bodies in the Saroki area of South Waziristan.
More than 35 soldiers have now died in the South Waziristan operation, along with a number of militants.
The army operation is focused on an area west of the town of Wana where they have cordoned off a large area in the search for foreign militants and tribesmen supporting them.
Tribal elders have been trying to negotiate the release of 14 more hostages held within the cordoned off area.
But they now say that Yargulkhel tribesmen, who have been fighting alongside the suspected al-Qaeda militants and who hold the hostages, have rejected a plea for the 14 to be freed.
The Yargulkhel tribesmen are insisting that they will not release the 14 hostages until the army ceases its operation in South Waziristan.
However, Pakistan's information minister, Sheikh Rashid Ahmed, says there will be no let up in the operation.
More troops would be sent to the area and the offensive would continue "whatever the cost may be", he said on Friday.
The military commander in charge of the Wana operation seemed to suggest that the mission of "destroying and denying sanctuary to militants" was nearing completion.
Protesters in Lahore condemn the army's South Waziristan offensive
Lieutenant-General Safdar Hussain told the Dawn newspaper he hoped operations would be wound up by Saturday.
On Friday, radical Islamic parties carried out a series of rallies across Pakistan to protest against the military operation in South Waziristan.
Small-scale rallies were held in dozens of cities.
Fazlur Rehman, the leader of the conservative alliance, the Muttahida Majlis-e-Amal, told a crowd in Peshawar: "Musharraf is a stooge of America and he has forced the army to kill Muslims in South Waziristan to please his masters."
The government launched the operation in order to tackle al-Qaeda and Taleban fighters and tribesmen suspected of sheltering them, and believed a "high-value target" was among them.
That figure was initially reported to be al-Qaeda deputy leader Ayman al-Zawahri, but the BBC's Paul Anderson in Islamabad says that if he was there it appears he has now escaped.
A tape recording released this week purportedly made by Mr Zawahri has urged Pakistan's Muslims to overthrow President Pervez Musharraf.
The CIA on Friday concluded the tape was probably authentic although the time of its recording was unknown.
The Pakistani information minister, Mr Ahmed, condemned the tape, saying: "Pakistan does not take orders from anybody. The entire nation is fully behind the policies of President Pervez Musharraf."