A suicide bomber who killed 101 people at a mosque in northwest Pakistan this week had disguised himself in a police uniform and did not raise suspicion among guards, the provincial police chief said on Thursday. Moazzam Jah Ansari said the bomber had been identified and police were close to arresting members of the network that was behind Monday's attack, one of the deadliest ever in Peshawar, the capital in the Khyber Pakhtunkhwa province. “We will avenge the martyrdom of each and every policeman," Ansari told a news conference. The blast collapsed the roof of the 50-year-old mosque, killing 101 people, mostly policemen. Two hundred twenty-five people were injured. Ansari spoke a day after dozens of police officers in a rare move joined a peace march organized by the members of civil society groups in Peshawar, demanding protection for themselves. Also read: Pakistan blames 'security lapse' for mosque blast; 100 dead Hours after the bombing, Pakistan's Defense Minister Khawaja Mohammad Asif accused the Pakistani Taliban, known by the acronym TTP, of carrying out the attack, saying they were operating from neighboring Afghan territory. Pakistan wants the Afghan Taliban to take action against the TTP group. Shortly after the bombing, a TTP commander claimed responsibility, but more than 10 hours after the attack the chief spokesman for the group distanced the TTP from the carnage, saying it was not its policy to attack mosques. On Wednesday, Afghanistan’s Taliban-appointed foreign minister, however, had asked Pakistani authorities to look for the reasons behind militant violence in their country instead of blaming Afghanistan. The comments from Amir Khan Muttaqi came after Pakistani officials said the attackers who orchestrated Monday’s suicide bombing were using Afghan soil to target civilians and security forces. More than 300 worshippers were praying in the Sunni mosque, with more approaching, when the bomber set off his explosives vest. Ansari said the attacker was not searched because guards assumed that he was one of their colleagues. “Yes, I admit that it was a security lapse and I take responsibility for it," Ansari said. Pakistan Prime Minister Shahbaz Sharif visited a hospital in Peshawar after the bombing and vowed “stern action” against those behind the attack. 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 in Pakistan since the Afghan Taliban seized power in neighboring Afghanistan in August 2021 as U.S. 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. ___ Associated Press writer Munir Ahmed contributed to this story from Islamabad