Gunmen broke into the house of a Pakistani official and killed 13 people near a northwestern town where Islamist militants are active, police said on Thursday.
The killings took place late on Wednesday in Gomal village, around 15 km southwest of the town of Tank in North West Frontier Province.
"We are investigating the motive behind the murder," Mumtaz Zareen, a senior police official in Tank, told Reuters.
The house belonged to Pir Aurangzeb, a senior official with the government-run power utility, WAPDA. Those killed included Aurangzeb, five members of his family and seven guests.
Violence has been increasing in parts of NWFP over the past year or so. Some analysts say that is evidence of "Talibanisation", or the spread of militant influence from remote tribal regions on the Afghan border to more developed, populous areas.
Militants, angered over Pakistan's support for the US-led war on terrorism, have killed a large number of government officials in recent years in the tribal regions.
Tank is the gateway to the South Waziristan tribal region near the Afghan border, known as a hotbed of support for al Qaeda and Taliban militants.
Islamist militants killed two paramilitary soldiers in a suicide bombing and another in an ambush near Tank on Monday.