At least 84 children were killed in Pakistan on Tuesday when Taliban gunmen stormed a military-run school in the city of Peshawar, taking hundreds of students and teachers hostage in the bloodiest insurgent attack in the country in years.

Troops surrounded the building and an operation was underway to rescue the remaining children, the army said. A Reuters journalist at the scene said he could hear heavy gunfire from inside the school.

Pervaiz Khattak, chief minister of Khyber Pakhtunkhwa, the province of which Peshawar is the capital, said 84 children had been killed.