A suicide blast claimed by the Islamic State group at a Shiite mosque in Islamabad killed at least 31 people Friday, with 169 others wounded in the deadliest attack in Pakistan’s capital since the 2008 Marriott hotel bombing.

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

The blast occurred during Friday prayers, when mosques across the country are packed with worshippers. “The attacker was stopped at the gate and detonated himself,” a security source said.

Islamic State said one of its militants targeted the congregation, detonating an explosive vest and “inflicting a large number of deaths and injuries,” according to the SITE Intelligence Group, which monitors extremist communications.

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

“During the first bow of the Namaz, we heard gunfire,” he said.

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

Another worshipper, Imran Mahmood, said 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 said.

He then detonated the explosives, Mahmood added.

Prime Minister Shehbaz Sharif vowed that those responsible would be found and brought to justice.

The attack was the deadliest in Islamabad since September 2008, when 60 people were killed in a suicide truck bombing that destroyed part of the Marriott hotel.

Bodies, bloodied clothing, debris

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

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

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

At the mosque, armed security forces cordoned off the area, where pools of blood were visible on the ground.

Yellow crime-scene tape surrounded the site, with shoes, clothing, and broken glass scattered nearby.

Videos shared on social media, which could not be independently verified, showed several bodies lying near the mosque’s front gate, with people and debris strewn across the red-carpeted prayer hall.

Deputy Prime Minister Ishaq Dar called 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.

U.N. 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 bordering Afghanistan.

Pakistan is a Sunni-majority country, but Shiites make up an estimated 10% to 15% of the population and have long been targeted by militant groups.

Islamabad has said separatist armed groups in southern Balochistan and Islamist militants in northern Khyber Pakhtunkhwa province use Afghan territory as a base for attacks.

Afghanistan’s Taliban government has repeatedly denied the accusations.

Relations between the two countries have deteriorated, with forces frequently clashing along the border.

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

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