Peshawar, Jan 31 : Terror returned to Peshawar with a suicide bomber blewing himself up at a mosque in Police Lines on Monday, killing dozens of people, mostly policemen. Officials confirmed that it was a suicide attack and that the bomber was standing in the front row at the time of the explosion. Peshawar Capital City Police Officer (CCPO) Muhammad Ijaz Khan said the bomber detonated his load at the moment hundreds of people had lined up for prayers. The latest attack targeting police ripped through the mosque during the prayers. The mosque is located inside a highly fortified compound in Peshawar that included the headquarters of the Khyber-Pakhtunkhwa (K-P) police force and the Counter-Terrorism Department (CTD) offices, The Express Tribune reported. "It was a suicide bombing," Khan said. The attacker appeared to have passed through several barricades manned by security forces to get into the "Red Zone" compound, he added. An inquiry was underway into how the attacker breached the elite security cordon and whether there was any inside help, The Express Tribune reported. Peshawar Commissioner Riaz Mehsood said a rescue operation was underway inside the mosque as a number of people were buried under the rubble. "We can't say how many are still under it," K-P Governor Haji Ghulam Ali later said. CCPO Ijaz also confirmed by nightfall that "a number of policemen were still stranded under the rubble and rescuers were trying to pull them out." "The mosque hall was packed with up to 400 worshippers, and most of the dead were police officers," he added, The Express Tribune reported. When asked about the nature of the explosives, the CCPO told reporters that "the smell of explosives has been detected but it is too early to say anything substantial". He added: "We have found traces of explosives." According to a preliminary investigation report, submitted to prime minister Shehbaz Sharif, the evidence collected from the blast site confirmed that the explosion was a suicide hit and a high-level committee had also been formed to investigate any security lapse, it added. The blast brought down the upper storey of the mosque, trapping dozens of worshippers in the rubble. The preliminary investigation report said that the roof collapsed because the explosion damaged the pillars of the mosque. /IANS