The IDF stepped up pressure on Hamas on Thursday, killing Interior Minister Said Siam and pushing deep into Gaza City as defense officials predicted a cease-fire would begin soon. Siam, the most senior Hamas political leader killed since Operation Cast Lead began on December 27, died along with his brother Iad, his son, and Gen. Salah Abu Shrakh, head of the Hamas General Security Service. The four were killed by an IAF strike on Iad Siam's home in Jabalya. Siam was the Hamas political echelon's liaison with the group's military wing, Izzadin Kassam, and was responsible for the various security apparatuses in the Strip, including the Hamas police and naval forces. Officials said he was one of the Islamist movement's more radical leaders and was a close associate of its Damascus-based chief Khaled Mashaal. According to Palestinian reports, Mahmoud Watfa, one of the commanders of Izzadin Kassam in Gaza City, was also killed in the strike. Three of Hamas Foreign Minister Mahmoud Zahar's bodyguards were killed by an IAF strike near his house in Gaza City early Thursday morning. Two weeks ago, the IAF killed Sheikh Nizar Rayyan, one of the top five Hamas leaders in Gaza and a senior member of Izzadin Kassam. IDF troops fought with Hamas gunmen throughout the day as they pushed deeper into Gaza City, taking up positions a few kilometers from downtown - the deepest push since the ground operation began on January 3. According to military sources, IDF troops shot and killed close to 60 Hamas gunmen. "The goal is to put pressure on Hamas," a senior military source said. Meanwhile, some 25 rockets hit the South, including two in Beersheba that wounded six people. A defense official said Israel was trying to advance before the expected implementation of an Egyptian-mediated cease-fire in the coming days. According to Palestinian reports, IDF tanks and infantry were taking up positions in the Gaza City neighborhoods of Basra and Tel Hawwa, and in the Shati (Beach) refugee camp. Thousands of people reportedly fled their homes as IDF forces advanced deep into the city, which has approximately 400,000 residents. Seven soldiers were lightly wounded during the day. On Thursday morning, IDF tanks fired shells at three high-rise buildings in Tel Hawwa. Palestinian reports said the army hit a multi-story building that houses several media outlets, including Reuters, Al-Arabiya and the BBC. Witnesses said that a Qatari journalist was wounded and that the building was evacuated. IDF sources said shots had been fired at troops from inside the building. IAF aircraft struck some 35 targets in the Strip throughout the day, including armed cells and rocket launch positions. Troops also opened fire at two UN vehicles in the Strip on Thursday. One of the cars, the IDF said, did not have markings identifying it as a UN vehicle. The other was marked as a UN car, but gunshots were fired from it at IDF troops, who returned fire. Earlier in the day, the IDF shelled the UN headquarters in the Gaza Strip after Givati Brigade soldiers came under anti-tank fire from gunmen standing next to the compound, defense officials said. The IDF responded by firing artillery shells at the gunmen, and it appeared that one of the shells accidentally hit a UN warehouse, setting it afire, the officials said. The IDF's Gaza Coordination and Liaison Administration coordinated the arrival of five fire trucks. Palestinians reported that an IDF tank shell also struck one of the wings of Al-Quds Hospital at midday. Witnesses said part of the structure was on fire. The army said that the building was being used by Hamas men who were firing at IDF troops. The International Federation of Red Cross and Red Crescent Societies said the damage caused to Al-Quds hospital was "completely and utterly unacceptable based on every known standard of international humanitarian law." The Geneva-based group said the second floor of the hospital had taken a direct hit that caused fires in the pharmacy and severe damage in many parts of the building. AP contributed to this report.