At least 31 people have been killed and 169 injured in an explosion at a mosque during Friday prayers in Pakistan's capital, Islamabad, according to a city official.

Police officials say a suicide bomber detonated a device after approaching the gates of the Shia mosque in the Tarlai area of the city, while eyewitnesses have told the BBC the blast was preceded by the sound of gunfire.

An emergency was declared as hospitals began to receive the wounded, with an appeal sent out for blood donations.

Pakistan's Prime Minister Shehbaz Sharif has condemned the incident, expressing "deep grief".

In a statement released on social media, he called for a thorough investigation and the immediate identification of those behind the attack.

Pakistan's President Asif Ali Zardari said in his own statement that "targeting innocent civilians is a crime against humanity".

'We bowed - then there was an explosion'

Zaheer Abbas was inside the Khadijatul Kubra Mosque praying when he first heard the sound of bullets.

"After that, we bowed and then prostrated, and then there was an explosion," he told BBC Urdu. "After which there were injured people lying everywhere."

Pictures from the mosque in the aftermath show footwear scattered across the floor, shattered glass, and people sat among the wreckage.

Abbas, who said he "lost his senses" in the moments after the explosion, was eventually pulled out by emergency services and taken to hospital, where he was quickly released.

"Fortunately, I did not suffer much injury," he said.

The mosque's caretaker Syed Ashfaq - who lives next door - also heard gunfire, and began running towards the mosque to help.

"By the time I reached it there had already been an explosion," he told the BBC. "Bodies were lying everywhere, some were missing arms, some missing legs. We took the most injured in our own vehicle [to hospital]."

Islamabad's deputy commissioner Irfan Memon said on X that the death toll stood at 31, with the injured numbering 169.

Pictures from local hospitals show the injured being brought by private vehicles and ambulances, with one photographer for news agency AFP saying they saw dozens of people arriving at hospital.

Attacks are relatively rare in the capital, although one in November left 12 dead. Another 27 were injured in the blast, outside a courthouse.

The blast on Friday comes after a week of violence which saw 58 civilians killed in coordinated attacks in the province of Balochistan.

The Balochistan Liberation Army (BLA) rebel group said it was behind the attacks. The military - which has been fighting an insurgency in the region for decades - said it had killed more than 200 militants in response.

Last year was also Pakistan's deadliest in over a decade as combat-related deaths surged 74%, with militants accounting for more than half the death toll, according to a new report released by an independent think tank.

The Pakistan Institute for Conflict and Security Studies (PICSS) said violence in Pakistan left 3,413 people dead - up from 1,950 in 2024 - with 2,138 militants killed.