More than 225 worshippers - many of them police officers - were left injured in the deadly explosion within a police compound in the northwestern city of Peshawar on Monday. Many still remained in critical condition in hospital.
The bomber detonated his explosives vest as crowds of around 300 people gathered for prayers - the roof caving in from the force of the blast.
Rescuers scrambled to remove mounds of debris from the mosque grounds to reach worshippers still trapped under the rubble, police said.
More bodies were retrieved overnight and early on Tuesday, according to Mohammad Asim, a government hospital spokesman in Peshawar, and several of those who were critically injured died.
"Most of them were policemen," he said of the victims.
Chief rescue official Bilal Faizi said rescue teams were still working at the site on Tuesday as more people were believed to be trapped inside.
Mourners were burying the victims at different graveyards in the city and elsewhere.
Counter-terrorism police are investigating how the bomber was able to reach the mosque, which is in a walled compound, inside a high-security zone with other government buildings.
Ghulam Ali, governor of the Khyber Pakhtunkhwa province, of which Peshawar is the capital, said: "Yes, it was a security lapse."
Talat Masood, a retired army general and senior security analyst said Monday's suicide bombing showed "negligence".
"When we know that Tehreek-e-Taliban Pakistan is active, and when we know that they have threatened to carry out attacks, there should have been more security at the police compound in Peshawar," he told The Associated Press, referring to a militant group also known as the Pakistani Taliban or TTP.
Sarbakaf Mohmand, a commander for the Pakistani Taliban, claimed responsibility for the attack on Twitter.
But hours later, TTP spokesperson Mohammad Khurasani distanced the group from the bombing, saying it was not its policy to target mosques, seminaries and religious places, adding that those taking part in such acts could face punitive action under TTP’s policy. His statement did not address why a TTP commander had claimed responsibility for the bombing.
Pakistan has seen a surge in militant attacks since November, when the Pakistani Taliban ended their cease-fire with government forces. Monday’s attack marked one of the deadliest attacks on security forces in recent years.
Police official Siddique Khan said the attacker blew himself up while among the worshippers, while the dead also included Noor-ul-Amin, the prayer leader.
Meena Gul, who was inside the mosque when the bomb went off, said he doesn’t know how he survived unhurt. The 38-year-old police officer said he could hear cries and screams after the bomb exploded.
Peshawar is the capital of Khyber Pakhtunkhwa province, where the Pakistani Taliban have a strong presence, and the city has been the scene of frequent militant attacks.
Muhammad Ijaz Khan, Peshawar capital city police officer, told local media that between 300 and 400 police officials were present in the area at the time of the blast.
The bombing has drawn nationwide condemnation from politicians and government officials.
Prime Minister Shahbaz Sharif denounced the bombing and vowed “stern action” against those behind the attack.
Former Prime Minister Imran Khan also condemned the bombing, calling it a “terrorist suicide attack” on Twitter. “My prayers & condolences go to victims families,” said the ex-premier.
“It is imperative we improve our intelligence gathering & properly equip our police forces to combat the growing threat of terrorism.”