Tank is the gateway to Pakistan's South Waziristan tribal region near the Afghan border, thought to be an area that shelters al-Qaeda and Taliban fighters.
 
Violence has been increasing in the province over the past year, with some analysts pointing to a rise in support for the Taliban.
 
Earlier this week, also in an area close to Tank, two paramilitary soldiers were killed in a suicide bombing and another in an ambush by armed men.