PESHAWAR, Pakistan - At least 18 people were killed and more than 40 wounded Friday when a bomb detonated in a bus filled with government employees and other civilians, authorities said. The bomb was believed to have been detonated by remote control, police said. "The victims included mainly government civilian employees and civilians," said Shafiullah Khan, a senior police officer at the scene. He said at least 22 employees of the Peshawar Civil Secretariat and more than 30 other civilian passengers were aboard the bus when the bomb went off as it was leaving this city in northwestern Pakistan near the border with Afghanistan. About 18 pounds of explosives were used in the blast, Khan said. No group has claimed responsibility for the attack so far. Mian Iftekhar Hussain, a spokesman for the Khyber-Pakhtunkhwa provincial government, told reporters at the blast site that four women and a child were among the dead. He said he could not immediately provide a confirmed toll of the dead and injured. But hospital sources said 18 bodies were brought to hospitals in Peshawar and the nearby town of Charsadda. Hussain attributed the attack to terrorism but said he did not see any immediate reason for it. "We want peaceful talks with the militants, but at the same time we will protect the lives of the people," he said. We will go after the militants even in North Waziristan to defeat them. Officials said eight bodies and 21 wounded passengers were taken to a government hospital in Charsadda. At least 10 dead bodies and nearly 20 injured were transported to Lady Reading Hospital in Peshawar. There has been a lull in terrorist attacks for past couple of months in the northwest, but security agencies fear more attacks on security forces and government installations in retaliation for the reported death of Abu Yahya al-Libi, the No. 2 leader in the al-Qaeda terrorist network, who was targeted in a U.S. drone strike Monday in North Waziristan near the Afghan border. U.S. officials said Libi was killed in the drone strike and described his death as a serious blow to al-Qaeda. But the Pakistani government has not yet confirmed publicly that Libi was killed. A security official, speaking on condition of anonymity because he is not allowed to talk to the news media, predicted two days ago that a terrorist attack would be carried out if Libi were confirmed dead. However, another intelligence official said the bus attack could be a reprisal for "military operations against Taliban militants in the tribal regions." Pakistani troops are conducting operations in the Mohmand and Khyber tribal areas bordering Afghanistan.