Several suspects have been arrested in connection with Monday’s suicide bomb blast in a mosque in Pakistan’s northern city of Peshawar that killed more than 100 people.

More arrests will take place following a major police investigation into the attack that injured another 217 people, Peshawar Police Chief Mohammad Aijaz Khan said.

Authorities are also investigating how the attacker entered the mosque, Khan added.

Families that live in the police compound where the mosque is located are being interrogated as police cannot rule out that the attacker may have been helped by someone internally.

Police suspect that 12 kilograms (26.5 pounds) of explosives were used by a suicide bomber, Inspector General of Peshawar Police Moazim Jah Ansari said earlier.

Footage emerged of the destroyed walls of the mosque, with glass windows and paneling pummeled in the powerful explosion.

Emergency workers searched through the rubble to locate survivors in the aftermath of the explosion, but authorities said “mostly dead bodies” were being found.

The blast Monday is indicative of the deteriorating security situation in Peshawar, capital of the restive Khyber-Pakhtunkhwa province that borders Afghanistan and the site of frequent attacks by the Pakistani Taliban, known as Tehreek-e-Taliban (TTP).

There were conflicting claims of who was responsible for the attack, with TTP officials Sarbakaf Mohmand and Omar Mukaram Khurasani initially saying the blast was “revenge” for the death of TTP militant Khalid Khorasani last year.

But the TTP’s main spokesperson, Muhammad Khorasani, later denied the group was involved in the attack.

Pakistan authorities have not confirmed either claim.

Rights groups denounced the attack, which came at a rocky period for Pakistan amid a grueling cost of living crisis and a faltering economy worsened by devastating floods last year.