PESHAWAR, PAKISTAN -- A suicide bomber who killed 101 people this week at a mosque in northwestern Pakistan had disguised himself in police uniform and did not raise suspicion among the guards, the provincial police chief said Thursday.

The bomber arrived pushing a motorcycle at the mosque, located inside a high-security police and government compound in the city of Peshawar, said the police chief, Moazzam Jah Ansari.

The bomber wore a police uniform and the guards at the site assumed he was a police officer -- their colleague -- and did not search him, Ansari added.

Police have identified the bomber, the police chief also said, and are close to arresting suspects who helped him carry out Monday's bombing, one of the deadliest ever in Peshawar, the capital of Khyber Pakhtunkhwa province.

"We will avenge the martyrdom of each and every policeman," Ansari told a news conference on Thursday, without providing more details. He pledged that all those responsible for the attack, including the mastermind and facilitators, will be arrested and punished under the law.

Pakistan's defense and interior ministers in speeches to Parliament this week blamed the Pakistani Taliban, who maintain sanctuaries in neighboring Afghanistan, for orchestrating the bombing. The Pakistani Taliban, known by their acronym TTP, are a separate group but allied with the Afghan Taliban.

Ansari said that most of the casualties -- the explosion also left 225 wounded -- were not caused by the detonation of the bomber's explosives but by the collapse of the roof of the 50-year-old Peshawar mosque. The force of the blast caused the roof, which was supported by outside walls but no pillars, to cave in.

Police also released footage, from police CCTV cameras, showing the suspected bomber, in police uniform, approaching the police compound pushing a motorcycle, giving the impression it had broken down.

"I admit that it was a security lapse and I take responsibility for it," Ansari said. He did not offer to resign his post.

On Wednesday, dozens of police officers in a rare move joined a peace march organized by the members of civil society groups in Peshawar, demanding better protection for police.

Pakistan's Defense Minister Khawaja Mohammad Asif and Interior Minister Rana Sanaullah Khan accused the Pakistani Taliban and in speeches to Parliament, said the TTP planned the attack from neighboring Afghanistan.

Pakistan has demanded the Afghan Taliban to take action against the TTP. Initially a TTP commander claimed responsibility for the suicide bombing but hours later the group's chief spokesman distanced the TTP from the carnage, saying attacking mosques was not its policy.

Meanwhile, Afghanistan's Taliban-appointed foreign minister urged Pakistani authorities to look domestically for the reasons behind violence in their country instead of blaming Afghanistan.

Pakistan's Foreign Ministry spokesperson Mumtaz Zahra Baloch appeared to dismiss the Afghan Taliban criticism.

"We take the loss of innocent lives very seriously and would expect our neighbors to do the same," Baloch told a news conference Thursday. "Pakistan expects sincere cooperation" from Afghanistan, he said.

Pakistan, which is mostly Sunni Muslim, has seen a surge in militant attacks since November, when the Pakistani Taliban ended a cease-fire with government forces. The violence has increased since the Afghan Taliban seized power in Afghanistan in August 2021.

Late Thursday, Prime Minister Shahbaz Sharif's government reached out to his predecessor and now opposition leader, Imran Khan, inviting him and other opposition politician to a conference next Tuesday to discuss how to respond to the surge in militancy across the country.

There was no immediate response from Khan, who was ousted in a no-conference vote in Parliament in April last year.

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Associated Press writer Munir Ahmed in Islamabad contributed to this story.