Four Lebanese soldiers were killed overnight as the army resumed Thursday shelling the remaining positions of al-Qaida-inspired Islamic militants entrenched in a Palestinian refugee camp in northern Lebanon, a senior military official said. The shelling by artillery and tanks lasted more than an hour, sending plumes of heavy black smoke billowing into the air, witnesses said. The army, meanwhile, announced the names of four soldiers it said were killed in fighting Wednesday with militants of the Fatah Islam group in the Nahr el-Bared camp on the outskirts of the northern port city of Tripoli. The senior military official, speaking on condition of anonymity because he was not authorized to talk to the media, said Wednesday's deaths raised to 111 the number of troops killed since fighting broke out in the camp two months ago. The army will continue its offensive until the militants surrender to Lebanese authorities, he said. The militants have vowed never to surrender. In response to the army's shelling, Fatah Islam fighters fired volleys of Katyusha rockets Thursday that landed in nearby villages, causing damage but no casualties, the state-run National News Agency reported. A Lebanese teenager was killed and a young girl was injured in Wednesday's Katyusha rocket attacks on villages near the camp. The use of Katyusha rockets appears to be a new tactic used by the militants to ease the army's pressure on its fighters. The Lebanese news agency said troops killed two snipers at dawn Thursday and captured "the Fatah Islam's main office" in an area where the militants remain holed up. The conflict with Fatah Islam militants is Lebanon's worst internal violence since the 1975-90 civil war. At least 60 militants and more than 20 civilians have been killed in the fighting, according to the Lebanese government and UN relief officials.