PESHAWAR, Pakistan: Pakistani authorities scrambled Tuesday to determine how a suicide bomber was able to carry out one of the country’s deadliest militant attacks in years, unleashing an explosion in a crowded mosque inside a highly secured police compound in the city of Peshawar. The death toll from the blast climbed to 100.Monday morning’s bombing, which left at least 225 wounded, raised alarm among officials over a major security breach at a time when the Pakistani Taliban, the main anti-government militant group, has stepped up attacks, particularly targeting the police and the military.Who carried out the bombing was unclear. A commander from the Pakistani Taliban, known by the acronym TTP, claimed responsibility, but a spokesman for the group later distanced the TTP from the carnage, saying it was not its policy to attack mosques.More than 300 worshippers were praying in the Sunni mosque, with more approaching, when the bomber set off his explosives vest, officials said. The blast blew off part of the roof, and what was left caved in, injuring many more, according to Zafar Khan, a police officer.Rescuers worked through the night and into Tuesday morning, removing mounds of debris to reach worshippers still trapped under the rubble. The death toll rose as more bodies were found and several of the critically injured died, said Mohammad Asim, a government hospital spokesman in Peshawar.Most of the victims were police officers, he said.Counter-terrorism police are investigating how the bomber was able to reach the mosque, which is inside a walled-off police headquarters compound called Police Lines. The compound is located in a heavily security district of Peshawar that includes other government buildings.”Yes, it was a security lapse,” said Ghulam Ali, the provincial governor in the Khyber Pakhtunkhwa province, of which Peshawar is the capital.Akhtar Ali Shah, a former regional interior secretary once based in Peshawar, said it “was not a spur of the moment attack.””It was the handiwork of a well-organized group,” he told The Associated Press. He said those behind the attack must have had inside help to gain access to the compound and probably entered it several times for reconnaissance or even to plant explosives ahead of time.”It’s not a security lapse, it’s a security breach,” he said. “From all entry points, there are multiple layers of security you have to cross” with ID checks.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 AP, using the official name of the Pakistani Taliban.The military’s media wing declined an Associated Press interview request for the chief of army staff. Asim Munir, who took office in November, has yet to do any media appearances.Kamran Bangash, a provincial secretary-general with the opposition Pakistan Tehreek-e-Insaf party, called for an investigation and blamed the instability on the government of Prime Minister Shahbaz Sharif.The government “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 party’s leader, former Prime Minister Imran Khan, denounced the attack.The bombing comes as Pakistan is contending with political and economic crises from a disputed election and from unprecedented floods last summer that killed 1,739 people, destroyed more than 2 million homes, and at one point submerged as much as a third of the country.Sharif visited a hospital in Peshawar after the bombing and vowed “stern action” against those behind the attack. On Tuesday he dismissed criticism of his government and called for unity. “My message to all political forces is one of unity against anti-Pakistan elements. We can fight our political fights later,” he tweeted.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.