A suicide bombing that killed dozens of police officers at a mosque in a government compound in north-west Pakistan reflects “security lapses”, officials have said.

The blast, which ripped through a Sunni mosque inside a major police facility in the city of Peshawar, was one of the deadliest attacks on Pakistani security forces in recent years.

The death toll rose to 100 on Tuesday, with more than 225 other people injured, many of whom remain in a critical condition in hospital.

More than 300 worshippers were praying in the mosque, with more approaching, when the bomber set off his explosives vest on Monday morning, officials said.

The explosion blew off part of the roof, and what was left soon caved in, injuring many more, according to police officer Zafar Khan.

Rescuers had to remove mounds of debris to reach worshippers still trapped under the rubble.

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 victim 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.

Kamkan Bangash, a provincial secretary-general with opposition party Pakistan Tehreek-e-Insaf, called for an investigation and said Pakistan will continue to face political instability as long as the current government is in power.

“The current government of Prime Minister Shehbaz Sharif has failed to improve the economy and law and order situation, and it should resign to pave the way for snap parliamentary elections,” he said.

The military’s media wing declined an Associated Press request for an interview with the chief of army staff. Asim Munir, who took office in November, has yet to do any media appearances.

Prime Minister Shahbaz Sharif visited a hospital in Peshawar after the bombing and vowed “stern action” against those behind the attack.

“The sheer scale of the human tragedy is unimaginable. This is no less than an attack on Pakistan,” he tweeted.

Authorities have not determined who was behind the bombing.

Shortly after the explosion, TTP commander Sarbakaf Mohmand claimed responsibility for the attack in a post on Twitter.

But hours later, TTP spokesman Mohammad Khurasani distanced the group from the bombing, saying it is 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, which is mostly Sunni Muslim, has seen a surge in militant attacks since November, when the Pakistani Taliban ended a ceasefire with government forces, as the country was contending with unprecedented floods that killed 1,739 people, destroyed more than two million homes, and at one point submerged as much as a third of the country.

The Pakistani Taliban are the dominant militant group in Khyber Pakhtunkhwa province, and Peshawar has been the scene of frequent attacks.

But the Islamic State in Khorasan Province, a regional affiliation of the Islamic State group and a rival of the Taliban, has also been behind deadly attacks in Pakistan in recent years.

Overall, violence has increased since the Afghan Taliban seized power in neighbouring Afghanistan in August 2021, as US and Nato troops pulled out of the country after 20 years of war.

The TTP is separate from but a close ally of the Afghan Taliban. It has waged an insurgency in Pakistan in the past 15 years, seeking stricter enforcement of Islamic laws, the release of its members in government custody and a reduction in the Pakistani military presence in areas of Khyber Pakhtunkhwa province it has long used as its base.

Earlier this month, the Pakistani Taliban claimed one of its members shot and killed two intelligence officers, including the director of the counter-terrorism wing of the country’s military-based spy agency Inter-Services Intelligence.

Security officials said on Monday that the gunman had been traced and killed in a shootout in the north-west, near the Afghan border.

In 2014, a Pakistani Taliban faction attacked an army-run school in Peshawar and killed 154, mostly schoolchildren.

The Taliban-run Afghan Foreign Ministry said it was “saddened to learn that numerous people lost their lives” in Peshawar and condemned attacks on worshippers as contrary to the teachings of Islam.

US Secretary of State Antony Blinken, who is on a visit to the Middle East, tweeted his condolences, saying the bombing in Peshawar was a “horrific attack”.

“Terrorism for any reason at any place is indefensible,” he said.

Pakistan is also contending with political and economic crises in the wake of the floods and a disputed election.

Condemnation also came from the Saudi Embassy in Islamabad, as well as the US Embassy, which said the “United States stands with Pakistan in condemning all forms of terrorism”.

UN Secretary-General Antonio Guterres called the bombing “particularly abhorrent” for targeting a place of worship, UN spokesman Stephane Dujarric said.

Former Pakistani prime minister Imran Khan also expressed his condolences, calling the bombing a “terrorist suicide attack”.