Peshawar, Pakistan - Peshawar's Army Public School, the site of a massacre that killed 141 people almost a month ago, has reopened amid tight security in the capital of Pakistan's Khyber-Pakhtunkhwa province.

Helicopters flew overhead as dozens of army soldiers patrolled the streets around the APS, tightly screening entry and exit points to the school, early on Monday morning.

Grim-faced soldiers stood guard as hundreds of children and their parents streamed into the school, where a memorial service was held in the presence of the country's army chief, General Raheel Sharif.

I will go back to the school. This determination is because my cousin was martyred. If I go to school, it is like I am challenging the terrorists. - Hasan Syed, 10, a survivor of the attack The mood among the students was sombre, but defiant, as they entered the premises. Many of the children were brought to the school in army trucks, which doubled up as school buses on the first day of school in the new year.

Access to the school was tightly controlled, with army soldiers standing guard on several pickets established in the streets around the school, as well at the graveyard immediately adjacent to it.

Deadliest attack

Particular attention was paid to the locality behind the school, from where at least seven gunmen broke into the premises on December 16, in an attack that saw them go room by room, killing 141 people in all, the deadliest attack in Pakistan's history.

More than 130 of those killed were students, many of them executed in their classrooms and in the school's main auditorium.

In the wake of the attack, Pakistan lifted a moratorium on executions in what it called "terrorism cases", and constituted military courts to try said cases.

The army also stepped up ongoing military operations in the country's tribal areas, where troops have been battling the Tehreek-e-Taliban Pakistan (TTP) and its allies since June.

The TTP claimed responsibility for the attack on the school in Peshawar, saying it was carried out in "revenge" for the alleged killing of women and children in the tribal areas by the military.

'Challenging the TTP'

"I think it is a good thing that the school is reopening," Tariq Aziz, 30, whose younger brother, Asad, was killed in the attack, told Al Jazeera. "Already time has been wasted, and the students' studies are suffering."

"Even if we are not safe, what can we do? We have to send our children to school. For the sake of their education."

Hasan Syed, 10, survived the attack, and was one of those who went back to the school on Monday.

"I will not be afraid of going back - I will go back to the school," he told Al Jazeera. "This determination is because my cousin [Asad Aziz] was martyred. If I go to school, it is like I am challenging the terrorists."

The reopening of the APS and other schools across Pakistan has been delayed several times, as authorities race to verify that adequate security arrangements are in place.

On Monday, thousands of schools reopened across the country, but many remained shut, as the government had not yet issued them certificates of approval for commencement of classes.

In Peshawar, 118 schools reopened on Monday, while a further 1,380 remained shut.

Follow Asad Hashim on Twitter: @AsadHashim