The Afghan branch of ISIS has claimed responsibility for the mosque bombing in the Pakistani city of Peshawar that killed at least 63 people attending Friday prayers.
The death death toll rose from 56 overnight as more of the 200 people wounded in the blast succumbed to their injuries.
A statement released by ISIS's Amaq News Agency said the attack was carried out by an Afghan suicide bomber from its affiliate in the region known as Islamic State-Khorasan Province.
The ISIS statement, translated by the SITE Intelligence group, identified the attacker and carried his picture. It said its fighters "are constantly targeting Shiites living in Pakistan and Afghanistan despite the intense security measures adopted by the Taliban militia and the Pakistani police to secure Shia temples and centres".
Pakistanis mourn victims of mosque suicide bombing
The bombing targeted a mosque in the Kucha Risalda area of Peshawar, a city close to the Afghan border in north-west Pakistan.
Moazzam Jah Ansari, the top police official for Khyber Pakhtunkhwa province where Peshawar is the capital, said the suicide bomber had a crude bomb packed with 5 kilograms of explosives strapped to his body.
Mr Ansari said the bomb was packed with ball bearings, which caused the high death toll.
Victims were taken to the Lady Reading Hospital in the city. Spokesman Asim Khan said the death toll was likely to continue to rise, with at least four patients in critical condition among the 38 still being treated.
He said the victims were peppered with shrapnel, several had limbs amputated and others were injured by flying debris.
Peshawar Police Chief Muhammed Ejaz Khan said the attacker opened fire on police outside the mosque in Peshawar’s old city, killing a policeman wounding and another.
Security camera footage showed the bomber moving quickly up a narrow street towards the mosque entrance wearing a large black shawl that covered much of his body. He fired at the police protecting the mosque before entering inside.
Within seconds, a powerful explosion occurred and the camera lens was obscured with dust and debris.
Prime Minister Imran Khan's national security adviser, Moeed Yusuf, said the bombing was a “heinous terrorist attack” and promised those behind the carnage would “be brought to justice".
“We will not allow our gains against terrorism and our internal security to be compromised at any cost,” Mr Yusuf said on Twitter.
Funerals for the victims began on Friday and continued into Saturday amid tight security. Police with sniffer dogs carried out body searches of mourners, who were then searched a second time by guards hired by the Shiite community.
Pakistan has experienced a significant increase in violence in recent months, including attacks on army outposts along the border with Afghanistan that have killed dozens of military personnel.
Many attacks have been claimed by the Pakistani Taliban, who analysts say have been emboldened by the Afghan Taliban seizing power last August in Afghanistan.
The Afghan Taliban condemned the Peshawar mosque attack. "There is no justification for attacking civilians and worshipers,” Taliban Deputy Minister for Culture and Information Zabihullah Mujahid said on Twitter.
Pakistan has urged Afghanistan’s new rulers to handover Pakistani Taliban militants who have been staging their attacks from Afghanistan. The Afghan Taliban said their territory will not be used to stage attacks against anyone, but until now have not handed over any wanted Pakistani militants.