Tribal armed men have killed at least 16 Pakistani soldiers in North Waziristan province, intelligence sources said.
Al Jazeera's correspondent in Islamabad quoted Pakistani security sources as saying the bodies discovered on Tuesday had been decapitated.
The soldiers, including commandos, were believed to have been killed on Sunday night.
An intelligence official told Reuters news agency: "Villagers found the bodies of the slain soldiers and reported it to army. Most of them were shot dead. Some of them had their throats cut."
The soldiers were killed in the Shawal area, 70km southwest of Miranshah, North Waziristan's main town.
Security sources also said four Pakistani soldiers had been injured in the province on Tuesday during clashes with pro-Taliban fighters in Data Kheil and Giler, near the borders with Afghanistan.
Violence
Northwest Pakistan has seen a wave of violence since July, when a peace deal with tribal leaders broke down in North Waziristan and the army assaulted Lal Masjid, or Red Mosque, in the capital Islamabad.
Northwest Pakistan has been seen a wave of violence since July, when a peace deal with tribal leaders broke down in North Waziristan and the army assaulted Lal Masjid, or Red Mosque, in capital Islamabad.
Several hundred people have been killed.
In neighbouring South Waziristan, tribal fighters are still holding about 250 soldiers who were captured late last month as they travelled in a convoy.
The fighters are demanding security forces pull out of the area and release some captured comrades.
Tribal elders have been trying to negotiate the release of the soldiers and one elder said on Tuesday he was optimistic some of the soldiers would be released on condition security forces promised to move out of three areas.
Maulana Merajuddin said: "We hope that the militants will release all or at least half of them tomorrow."