ISLAMABAD - At least 12 students were killed and 35 others injured as 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, reported local Urdu TV channel ARY quoting hospital sources.

An unknown number of students and staff members of the school were also held hostage by the attackers, reported local media.

The Pakistani Taliban have claimed responsibility for the attack.

According to local officials and media reports, an estimated four to six militants wearing army uniforms launched the attack at the army-run public school located on Warsak Road in Gulbahar area of Peshawar at about 10:30 am (local time) on Tuesday.

The school, named Army Public School Peshawar, is run by the army and mainly offers education to children of the army families aged from five to 17.

They stormed the school from the back entrance and firing was heard during their attack, said eyewitnesses.

The army and other security forces have surrounded the school shortly after the attack was reported, said local media.

An exchange of firing between the militants and the security forces is still going on inside the school, confirmed army sources.

The attackers held an unknown number of students and staff members in the school's auditorium, said teachers of the school.

All the injured have been shifted to Lady Reading Hospital in Peshawar. Hospital sources said some of the injured were in critical condition.

Pakistani Prime Minister Nawaz Sharif have condemned the attack and directed the concerned authorities for the early and safe recovery of the students and staff.