The Pakistani military pounded an extremist stronghold near the Afghan border where a rebel leader blamed for the assassination of former Prime Minister Benazir Bhutto is believed to be hiding, officials and witnesses said. The strikes Sunday came a day after authorities said they had arrested a 15-year-old boy in northwestern Pakistan alleged to have been involved in the Dec. 27 slaying of Bhutto, an opposition leader critical of rising Islamic extremism in the country. The central government has never had much control over South Waziristan, a tribal area where several top militants are believed to live. They included Baitullah Mehsud, a Pakistani accused by the government and the CIA of masterminding the killing of Bhutto. Officials said the boy had confessed to taking part in a plot to kill Bhutto in a gun and suicide bomb attack in the garrison town of Rawalpindi. His role in the mission to kill Bhutto was as a backup in case the shooter or the suicide attacker failed, according to an intelligence official who has seen his interrogation records. The boy said the slaying was organized by Mehsud, who has previously denied any involvement in the attack, according to the official who spoke on condition of anonymity because he was not authorized to release the information. Authorities say the boy received terrorist training in neighboring Afghanistan before taking part in the mission. He told interrogators he trained for 40 days in a camp run by Mehsud in the Kotai area of South Waziristan before going to Helmand province Afghanistan in 2007 for another 40 days of "practical training." Meanwhile, Sunni extremists fired small arms and mortars at a Shiite procession commemorating Ashoura, a Shiite Muslim holiday that is often scarred by sectarian violence, the military said in a statement. Nine civilians and three security troops were injured in the incident in northwestern Hangu town, which ended after troops fired tear gas from a helicopter, it said. Two civilians were killed and five others wounded in the attacks near the border close to the towns of Lhada and Makin in South Waziristan, said Fazal Subhan, a Makin resident. However, military spokesman Maj. Gen. Athar Abbas said there were no reports of casualties in the operations. Fighting in South Waziristan in recent days has killed more than 100 soldiers and militants. The violence, including suicide attacks that have killed hundreds in recent months, comes as the nuclear-armed country prepares for Feb. 18 elections that many predict will weaken President Pervez Musharraf's grip on power. Other than the incident in Hangu, Ashoura appeared to pass peacefully in the country of 160 million Muslims.