ISLAMABAD, Dec. 16 -- At least 84 people had been killed and 83 others injured when a group of militants launched an attack on an army-run public school in Peshawar of Pakistan's northwest Khyber Pakhtunkhwa Province on Tuesday morning, a senior official of the province said.

Chief Minister of the province, Pervez Khattak, said the killed include 81 students, two teachers and a security personnel.

Apart from this, an unknown number of students and staff of the school are still being held hostage by the attackers, said local media.

Three militants have so far been killed in exchange of firing with the security forces who have rounded up them inside the school shortly after the attack was reported, said army sources.

Pakistan Taliban have claimed responsibility for the attack.

Pakistani Prime Minister Nawaz Sharif has flown to Peshawar to direct the rescue operation. Army Chief Gen. Raheel Sharif has also cut short a visit to the country's southwest province Balochistan and headed for Peshawar.

Pakistani President Mamnoon Hussain has issued a statement strongly condemning the attack and said such coward attacks cannot deter the resolve and morale of the Pakistani nation to fight against terrorism.

The attack reportedly took place at about 10:30 a.m. (local time) when a group of eight to ten Taliban militants wearing army uniforms launched an attack at an army-run public school in the downtown area of Peshawar. The school offers education mainly for children aged from 9 to 16 from the army families.

By the time when the story is being filed, the exchange of firing between the attackers and the security forces is still going on.