The family was going for a wedding party from Peshawar to Dera Ismail Khan when their ill-fated van caught fire on Indus Highway following a huge explosion while passing through Karak district, Javed Khan, police chief of Karak said.
Seven women and five children were killed while six others were injured in the fatal accident.
The injured were rushed to a nearby hospital where their condition was stated to be stable, Khan said adding that road was blocked for vehicles after the accident.
Thousands of vehicles in Pakistan run on gas cylinders which often burst resulting in casualties.
Poor road infrastructure and reckless driving are the leading causes of accidents in Pakistan.