Iftikhar Ahmad, district police officer of Hangu said a religious school, Madrassa Dar-ul-Uloom, was targeted by the US drones, and those killed include four students and two Islamic scholars who were believed to be associated with the banned militant outfit Haqqani network, Xinhua reported.
He said that the killed scholars included Mufti Hameed Ullah and Mufti Ahmad Jan who had very good relations with the Haqqani network.
Some local media reports said that a senior leader of the Haqqani Network visited the seminary a few days ago, and some of their fighters receive religious education from the targeted scholars.
The US drones fired four missiles at the seminary that was located in Thall area of Hangu, a main district in the country's northwest Khyber Pakhtoonkhwa province.
The US often launches missile strikes from drones in Pakistan's semi-autonomous lawless tribal belt to kill Taliban militants, but it is the first time that missiles were fired in the settled area of Hangu.
The US often launches missile strikes from drones in Pakistan.
Some media reports earlier claimed that the drone strike happened in the tribal area of North Waziristan, but officials later confirmed that the missiles fired from drones landed in Thall area located along the border of Hangu and North Waziristan.
The strikes were launched at about 5 a.m. when an unknown number of religious students were inside the seminary that was levelled to the ground following the attack.
People nearby rushed to the site of the incident and rescued five injured people from the rubble.
This was the first drone attack in the country after the Nov 1 when Taliban chief Hakimulla Mehsud was killed in a US drone strike.
The Nov 1 attack seriously affected the efforts of peace-talks between the Taliban and the Pakistan government.
Thursday's attack came a day after Sartaj Aziz, Pakistan Prime Minister Nawaz Sharif's advisor on foreign affairs and national security, said in a briefing to a senate committee that the US had assured Pakistan that it would not launch any drone strikes during the peace-talks between the Pakistan government and the Taliban.