PESHAWAR— At least 57 people were killed and more than 100 wounded on Friday after an explosion tore through a Shiite mosque in Peshawar, in northwestern Pakistan, according to the police and doctors at the city’s main hospital.
Police officials said that they were still piecing together what happened, but that at least one gunman on a motorbike had killed two police guards before entering the mosque and detonating what appeared to be a suicide vest.
The attack was one of the deadliest in years to hit Peshawar, a city of roughly two million people near Pakistan’s border with Afghanistan. In 2014, nine Taliban gunmen killed more than 140 people at the Army Public School and Degree College there.
“We are trying to figure out and determine what happened,” Moazzam Jah, the provincial police chief, said on Friday. A Capital City Police officer, Ejaz Khan, said the police had recovered pallets, empty bullet cartridges and pieces of the gun used in the initial attacks.
Mr. Khan said there appeared to have been two assailants, both of whom had worn and detonated explosives. “We have secured CCTV footage and will be examining it very closely,” he said.
Area residents said they heard a huge blast in the main mosque in Kocha Risaldar, a largely Shiite neighborhood in the city.
The police cordoned off the mosque while rescue workers took the dead and wounded to the main hospital, Lady Reading.
A spokesman for the hospital, Muhammad Asim Khan, said that 10 of those people were “in very critical condition.”
No group has yet claimed responsibility for the blast, but Pakistani intelligence officials said on Friday that the attack was most likely carried out by the region’s Islamic State affiliate, Islamic State Khorasan, or ISIS-K.
“We see the ISIS-K as the biggest threat, bigger than the outlawed militant Pakistani outfit, the Tehreek-i-Taliban Pakistan,” Mr. Jah said.
Islamic State Khorasan announced its formation in eastern Afghanistan in 2015 and was initially led by former members of the Pakistani Taliban. Last fall, the Islamic State group carried out high-profile bombings at two Shiite mosques in Afghanistan, killing and wounding dozens.
The Afghan Taliban, after their rise to power in August, launched a series of operations against the group, possibly prompting its fighters to shift their operations into Pakistan, the intelligence officials said.