At least 57 people have been killed and another 195 injured, many critically, in an explosion that took place while Friday prayers were underway at an imambargah plus mosque located in the historic Qissa Khawani bazaar of Peshawar, Aaj News reported.

Lady Reading Hospital spokesperson Muhammad Asim confirmed that the death toll has risen from 30 to 57 and 194 injured, including several with critical injuries, were brought to the hospital.

The official account of Peshawar police tweeted that two assailants were involved in the attack on the Shia Jamia Mosque, and they exchanged fire with police deployed at the entrance door.

"One policeman was martyred and another was injured in the firing. His condition is critical," it added.

One eyewitness told Aaj News that he saw an alleged attacker clad in black open fire at the place of worship in the Koocha Risaldar area, and then detonated a suicide vest.

There are reports that at least one of the attackers tried to make his way to the pulpit, with the imam

The windows of the three-storey mosque have been shattered due to the intensity of the blast, while the steel frame of the entrance has also been damaged.

According to reports, children and the elderly are among the injured, including some that are critically hurt.

People have rushed to the Lady Reading Hospital to help authorities in the process of identification of the deceased.

Rescue authorities are at the scene of the explosion, which occurred in a part of the market with narrow lanes, congested streets and high footfall. Locals initially joined the rescue efforts and visuals from the site showed people transporting the injured to ambulances.

A large contingent of security forces are also on the scene and efforts are underway to cordon off the area.

CCPO Peshawar Muhammad Ijaz Khan, while speaking to Aaj News, said that the attackers riding on a motorcycle arrived at the imambargah. They exchanged fire with the policemen deployed at the entrance in which one of the policemen was killed while the other was critically injured.

Authorities have cleared the area and cordoned off the imambargah and mosque, while law-enforcement personnel are collecting evidence from the site of the blast.

PM Imran has condemned the attack while expressing condolence over the heavy loss of lives. He has also sought a report on the security breach while ordering the provision of medical facilities to the casualties.

Interior Minister Sheikh Rashid has confirmed that it was a suicide attack.

So far no group has claimed responsibility for the attack.

Khyber-Pakhtunkhwa Chief Minister Mehmood Khan has also sought a report of the explosion while ordering law-enforcement authorities to ensure those responsible for the heinous act are brought to book.

Condemnation and condolences continue to pour in from the country's political leadership, with PPP Chairperson Bilawal Bhutto Zardari, PML-N leader Maryam Nawaz and Foreign Minister Shah Mahmood Qureshi condemning the terrorist attack. President Alvi also lamented the loss of lives.

IS claim

Late on Friday night, AFP reported that the militant Islamic State group had claimed the suicide bombing in Peshawar.

“Today ... an Islamic State fighter succeeded in assaulting a Shia mosque in Peshawar,” the group said on its Amaq propaganda site.

Even before the claim came to light, security officials were of the view that the attack bore the hallmarks of the Islamic State group’s Khorasan chapter.

“We see the IS-K as the biggest threat, more than the outlawed Tehreek-i-Taliban Pakistan,” Mr Ansari, the Peshawar inspector general of police, said.

The IS-K is based in Afghanistan, but security officials say the anti-Shia terrorist group appeared to have shifted focus to Pakistan after coming under intense pressure from the Afghan Taliban.

Friday’s attack was the biggest terrorist activity in the city.