Militants opened fire on a convoy of passenger vans heading for the neighboring Kurram tribal region, killing ten people, including two children and three women on Friday.
The death toll is expected to rise as some of the injured are in critical condition, medics said.
This is the third incident of its kind in Hangu this month.
Some reports have revealed grave instances of human rights abuse against Shias in the northwestern Pakistani city of Parachinar in Kurram agency.
Although Shias are the majority in Kurram, they are surrounded by the Taliban-linked aggressive militants who have gone so far as to cut off roads over the past few months. The militants are also accused of kidnapping or killing those trying to deliver supplies to the Shia areas.
Shia farmers have been forced to sell their agricultural produce in Afghanistan instead of the markets in Pakistan's North West Frontier Province.
Taliban-linked militants in Parachinar, Hangu district and much of the Kurram tribal agency have killed 25 to 30 people on a daily basis over the last six months. Some local media say more than 1,300 Shia community members have been killed in the region since 2007.
They claim that security forces in the tribal regions are 'under the influence of local Taliban groups', adding that law enforcement officers have 'willingly or unwillingly' launched a clamp down on Shia Muslims.
The killing of Shias is to such extent that has caused international outrage with rights groups and regional countries including Iran expressing concern over the 'genocide'.
Despite an offensive by the Pakistani government against pro-Taliban militants, they have spread their influence in various regions, killing people and security forces every day.
More than 4,000 people have died in bomb attacks across Pakistan since 2007.
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