A blast at a mosque inside a police headquarters in Pakistan on Monday killed at least 17 worshippers and wounded 80 more, hospital officials said.
The incident happened during afternoon prayers in the northwestern city of Peshawar near the border with Afghanistan.
Part of the mosque roof and wall had collapsed and bloodied survivors limped from the wreckage, as dead bodies were ferried away in ambulances, an AFP reporter saw.
"It's an emergency situation," Muhammad Asim Khan, a spokesman for the main hospital in Peshawar, told AFP.
He said the facility had so far received 17 patients dead-on-arrival while several of the 80 injured were in critical condition.
Many worshippers were still trapped inside, police said, and heavy machinery and fire brigades were combing the ruins for survivors in a frantic rescue operation.
Officers said the blast emanated from the second row of worshippers, with bomb disposal teams probing the possibility of a suicide attack.
Pakistan's rugged northwestern region has long been a hive of militant activity, a place where successive governments have struggled to establish a writ.
Last March, an Islamic State suicide bomber attacked a minority Shiite mosque in Peshawar killing 64 in Pakistan's deadliest terror attack since 2018.
The domestic chapter of the Taliban – known as Tehreek-e-Taliban Pakistan (TTP) – are also active there.
Since the Taliban surged back to power in Afghanistan, Islamabad has accused them of failing to secure their mountainous border, allowing fighters to flit back and forth to stage attacks and escape capture.
Over the first 12 months of Taliban rule in Afghanistan, Pakistan witnessed a 50 percent surge in militant attacks, focused in the western border provinces, according to the Pak Institute for Peace Studies.
Detectives said the March 2022 Islamic State bomber in Peshawar was an Afghan exile who had returned home to train for the attack.
Peshawar was also the site of a 2014 massacre by the TTP, who raided a school for children of army personnel and killed nearly 150 people, most of them pupils.