Karni crossing opened on Sunday afternoon to allow 150 trucks a day for the next four days into the Gaza Strip, carrying vital supplies and fuel. Fearing a humanitarian crisis in the Gaza Strip, Defense Minister Amir Peretz ordered Saturday night that the crossing be reopened for humanitarian aid. The move came as large military forces remained poised near Kibbutz Mefalsim southeast of Sderot, awaiting orders from the political echelon regarding a planned incursion into the northern Gaza Strip. Over the weekend, the IDF kept up the pressure on the Hamas kidnappers of Cpl. Gilad Shalit with continuous missile and artillery strikes on open areas in northern and southern Gaza. Sources in the Prime Minister's Office said these type of strikes would continue. The officials said the Gaza effort was an "ongoing operation" and that Prime Minister Ehud Olmert had said at the outset that it would be of "long" duration. IAF aircraft demolished seven main roads in the southern Gaza Strip on Saturday in an effort to thwart attempts by Hamas terrorists to move Shalit. Palestinians reported that Shalit had been wounded in the attack on his IDF outpost last Sunday but had been treated by a local doctor and was in good condition. Military sources said the IDF was ready to enter the northern Gaza Strip but was waiting for the green light from Olmert. The IDF had planned to invade northern Gaza on Thursday but the operation was postponed by Olmert, who decided to give Egyptian diplomatic efforts one last chance. On Saturday, Peretz urged US Secretary of State Condoleezza Rice to step up pressure on Syria, which he said was the "address" for a quick solution to the tense situation in the Gaza Strip. "Syria cannot evade responsibility for the kidnapping," Peretz told Rice. He asked her to urge Syrian President Bashar Assad to use his influence over Damascus-based Hamas chief Khaled Mashaal to assist in the speedy release of Shalit. The IDF fired nearly 500 artillery shells at Kassam launch sites in northern Gaza over the weekend. On Friday, IAF missiles struck a car traveling in Gaza City, causing a large explosion and wounding three Palestinians, one seriously. The IDF confirmed it had fired the missiles, saying the men in the car were Islamic Jihad terrorists on their way to fire Kassam rockets at Israel. Also Friday, IAF fighter jets struck offices of the Palestinian Authority's Interior Ministry and of Fatah in Gaza City. Missiles also hit a Hamas training camp on the outskirts of the city. Other targets struck by missiles included a Kassam rocket production warehouse affiliated with Fatah's Aksa Martyrs Brigades. The IDF said it had decided to attack the Interior Ministry building because it was used as "a meeting place to plan and direct terror attacks against Israel." Early Friday morning, an IAF helicopter near Gaza's destroyed airport in the southern Gaza Strip fired upon and fatally wounded Abdel Rael, 25, an Islamic Jihad member who was attempting to fire a rocket at IDF soldiers. His death marked the first fatality since the IDF's operation to free Shalit began on Tuesday. The IDF said in a statement that the strikes would continue as long as Hamas terrorists refused to release him. Herb Keinon contributed to this report.