The bullet-riddled bodies of four men have been found in northwestern Pakistan, near the Afghan border.
Pakistani officials said Saturday the bodies were discovered along a road in the town of Karak, in North Waziristan.
They said a note attached to the bodies warned the same fate awaited anyone who spies for the United States.
North Waziristan is a stronghold of Pakistani Taliban and al-Qaida militants who stage cross-border attacks on U.S.-led NATO forces in Afghanistan.
The U.S. has increasingly been using unmanned aircraft to bomb militants in the area.
Elsewhere, a car bomb in the Khyber tribal district killed three passengers and two pedestrians.
Local officials say the bomb detonated Saturday as the car traveled near the village of Barqambarkhel.