Israel dispatched reserve units to the Gaza Strip on Sunday as the IDF was said to be carving out a "security zone" along the border, which it would retain even after an end to the fighting and use to conduct routine patrols aimed at halting rocket attacks against the South. Senior defense officials told The Jerusalem Post on Sunday that while diplomatic efforts were picking up speed, Israel was likely to "expand" the operations in Gaza before agreeing to a withdrawal and cessation of operations against Hamas. On Sunday, IDF tanks and infantry units pushed deeper into Gaza City, encountering fierce Hamas resistance and killing, according to the military, close to 50 Hamas operatives. Earlier in the day, the IAF bombed the home of Ahmed Ja'abri, commander of the Hamas military wing. Ja'abri was not believed to be home at the time. The IDF would not say whether the insertion of the reserve forces constituted the much-anticipated "third phase" of Operation Cast Lead, which is believed to be either a deeper incursion into Gaza City or an expansion of operations in other parts of Gaza including in the south. "We will escalate operations before pulling out," a senior defense official told the Post. "There is still more to do in order to achieve our goals and hurt Hamas's military wing more significantly." A senior military officer who is commanding forces fighting inside Gaza said on Sunday that Hamas terrorists were trying to cross the line the IDF had created separating northern Gaza from the south. Some attempts to cross the line, he said, were made by Hamas gunmen hiding inside Red Crescent ambulances. The IDF said that Hamas's use of civilian infrastructure to carry out its attacks had increased in recent days. On Sunday, the IDF spokesperson released video footage showing how Hamas had booby-trapped a school and zoo in Gaza City's Zeitun neighborhood. The booby-trap was first reported in the Post last week when it was discovered by troops from the Givati Brigade who had slept inside a school and awoke in the morning to discover that the school, located adjacent to the zoo, was wired with explosives that were miraculously not triggered. Defense Minister Ehud Barak visited the Golani Brigade's command center outside of the Gaza Strip, and said that Israel would continue its operations as it continued to review several cease-fire proposals. Meanwhile Sunday, in the fiercest ground battles since the start of the operation, IDF troops fought against Palestinian gunmen in the Gaza City suburb of Sheikh Ajleen. Fighting in Sheikh Ajleen erupted before dawn and continued into the day as IDF infantrymen and tanks advanced toward the neighborhood of Gaza City and its approximately 400,000 residents, Palestinian witnesses said. Hamas and Islamic Jihad said they ambushed the soldiers, leading to some of the heaviest fighting since Israel sent ground forces into the territory on January 3. Gunfire subsided in the early afternoon, with the IDF in control of buildings on the neighborhood's outskirts. At least 40 Palestinians had been killed across Gaza by Sunday afternoon, according to Gaza health officials. Many were noncombatants, they claimed, including four members of one family killed when a tank shell hit their home near Gaza City. On Sunday, the IAF dropped additional leaflets urging Gaza residents to report the whereabouts of Hamas operatives, even providing a phone number to call. "You can call the numbers listed below to inform us about the locations of rocket launchers, warehouses, tunnels and terrorist groups operating in your area," the leaflet said in Arabic, promising "confidentiality guaranteed." On Saturday, flyers were dropped on Gaza City warning residents of a wider offensive. "The IDF is not working against the people of Gaza but against Hamas and the terrorists only," the flyer said. "Stay safe by following our orders." Also on Sunday, the IAF hit at least seven rocket cells, as well as the launcher used to fire the Grad-type rockets at Beersheba on Sunday morning. In searches in the northern Strip on Sunday the IDF found several weapons caches, one of them containing communications equipment.