A suicide blast at a Shiite mosque in Islamabad killed at least 31 people on Friday, with 169 more wounded, in the deadliest attack in Pakistan's capital since the 2008 Marriott hotel bombing.

City officials said 31 people died in the blast at the Imam Bargah Qasr-e-Khadijatul Kubra mosque in the Tarlai area on the city's outskirts, with scores more being treated for injuries. The death toll was expected to rise further.

The explosion occurred during Friday prayers, when mosques around the country are packed with worshippers.

"The attacker was stopped at the gate and detonated himself," a security source told AFP.

Muhammad Kazim, a 52-year-old worshipper, said an "extremely powerful" explosion ripped through the building as prayers were just starting.

"During the first bow of the Namaz (prayer ritual), we heard gunfire," he told AFP.

"And while we were still in the bowing position, an explosion occurred," he said.

Another worshipper, Imran Mahmood, told AFP there was a gunfight between the bomber, a possible accomplice, and volunteer security personnel at the mosque.

"The suicide attacker was trying to move forward, but one of our injured volunteers fired at him from behind, hitting him in the thigh," he told AFP.

He then "detonated the explosives," Mahmood, in his fifties, added.

No group immediately claimed responsibility, while Prime Minister Shehbaz Sharif said those behind the blast would be found and brought to justice.

South Asia analyst Michael Kugelman said on X that the target suggested it was either the local affiliate of the Islamic State group or anti-Shiite militants.

The attack was the deadliest in the Pakistani capital since September 2008, when 60 people were killed in a suicide truck bomb blast that destroyed part of the five-star Marriott hotel.

Bodies, bloodied clothing, debris

AFP journalists at the Pakistan Institute of Medical Sciences hospital saw several people, including children, being carried in on stretchers or by their arms and legs.

Medics and bystanders helped unload victims with blood-soaked clothes from the backs of ambulances and vehicles. At least one casualty arrived in the boot of a car.

Friends and relatives of the wounded wept and screamed as victims—dead or alive—arrived at the hospital's heavily guarded emergency ward.

Another team of AFP journalists saw armed security forces outside the mosque, where pools of blood were visible on the ground.

Yellow crime scene tape surrounded an investigation area, with shoes, clothing, and broken glass scattered around the site.

Videos shared on social media, which AFP was not able to verify immediately, showed several bodies lying near the mosque's front gate, with people and debris also strewn across the red-carpeted prayer hall.

Deputy Prime Minister Ishaq Dar branded the attack "a heinous crime against humanity and a blatant violation of Islamic principles."

"Pakistan stands united against terrorism in all its forms," he said in a post on X.

UN Secretary-General Antonio Guterres said "attacks against civilians and places of worship are unacceptable," according to his spokesman.

Growing insurgencies

The attack comes as Pakistan's security forces battle intensifying insurgencies in southern and northern provinces that border Afghanistan.

Pakistan is a Sunni-majority nation, but Shiites make up between 10 and 15 percent of the population and have been targeted in attacks throughout the region in the past.

Islamabad has said separatist armed groups in southern Balochistan, and the Pakistani Taliban and other Islamist militants in northern Khyber Pakhtunkhwa province near Islamabad, have used Afghan territory as a safe haven from which to launch attacks.

Afghanistan's Taliban government has repeatedly denied Pakistan's accusations.

Bilateral relations have plummeted, with forces from both sides regularly clashing along the border.

The last major attack in Islamabad took place in November, when a suicide blast outside a court killed 12 people and wounded dozens—the first such incident to hit the capital in nearly three years.

In Balochistan, attacks claimed by separatist insurgents last week killed 36 civilians and 22 security personnel, prompting a wave of counter-operations in which authorities said security forces killed almost 200 militants.