IDF tanks moved to within 500 meters of Gaza City on Saturday night, as Israel maintained its siege on the Strip in an effort to rescue kidnapped Cpl. Gilad Shalit and stop Kassam rocket attacks on the western Negev. Approximately 20 Palestinians were killed over the weekend, bringing the total number of dead to close to 50 since the IDF launched Operation Alonei Bashan in northern Gaza, IDF sources said. Meanwhile, Golani infantrymen pulled out of Atatra in northern Gaza, where most of the toughest fighting had taken place following the IDF entrance before dawn Thursday into the area. According to the IDF, about 50 Palestinians, most of them armed, were killed during the fighting there. St.-Sgt. Yehuda Basel of the Golani was killed by friendly fire, and two soldiers were wounded. The current focus of the IDF operation, sources said, was farther south near the Karni crossing, where some 15 tanks took up positions together with armored vehicles carrying Givati infantry. The force, officers said, was searching for suspected terrorist tunnels. Troops were also stationed at the abandoned Dahaniye airport. Most Palestinians killed in the offensive have been gunmen, but Palestinians claimed the dead included civilians, including an 11-year-old boy. Dozens of Palestinians have been wounded. Hundreds of mourners marched through Gaza City Saturday carrying victims of the fighting wrapped in green Hamas flags. Some shouted for revenge against Israel. Others fired guns in the air. "We warn the Zionist enemy not to invade Gaza again. We have prepared surprises for them if they do," a Hamas member said. Also Saturday night, Palestinians said that an IDF artillery shell had exploded in a house on the outskirts of Gaza City and killed three members of a family, including a six-year-old girl. The IDF denied responsibility and said its artillery had not been firing in the area. However, the army acknowledged that a missile had been fired in the area shortly beforehand, and was checking if the incidents were connected. OC Southern Command Maj.-Gen. Yoav Gallant said Saturday that the IDF was prepared to remain in Gaza for up to two months if necessary. "We are ready to continue this operation for a month, two months and if needed even more," Gallant told Channel 2's Meet the Press. He expressed confidence that the IDF would deal a severe blow to the terrorist infrastructure in Gaza and would cause the Palestinians to think twice before launching attacks against Israel. "When they see in a month from now that hundreds of terrorists are dead and that their terror infrastructure is destroyed... I am sure they will think again before launching another attack or kidnap attempt," he said. Golani Brigade commander Col. Tamir Yidai said Saturday night that the Palestinians had already been dealt a harsh blow. "During the 48 hours that we were in Gaza we killed between 40 and 50 [gunmen]," he said. "This is no doubt a significant blow for them." While the IDF has pulled out of northernmost Gaza, sources said operations there would be renewed. The Golani battalions that pulled out on Saturday, the source said, were now resting and waiting for new orders. The operations in Gaza were planned as rapid strikes in and out of the Strip, the source said, to minimize intensive combat in urban areas. Yidai said it was possible the army would expand its presence in the Strip. "The Palestinians understand that we can deepen our incursion if we want to," he said. On Saturday, the IAF fired missiles at a group of terrorists in the outskirts of Gaza City's Shajaiyeh neighborhood. Three Hamas gunmen were killed in the strike, hospital officials said. Another man, reportedly a policeman, died of wounds sustained in earlier fighting. In the first operation of its kind, IAF aircraft destroyed a tunnel that Palestinians had dug beneath the Karni crossing early Saturday morning. The entrance to the tunnel had been concealed inside a chicken coop. The IAF carried out four other air strikes in Gaza overnight Friday, targeting terror cells. Meanwhile Friday, 17 Kassam rockets were launched into the western Negev, falling near a number of kibbutzim, including Sa'ad, Nahal Oz, and Gevim, as well as near the town of Netivot, Army Radio reported. Two Kassams landed in Sderot and seven people were wounded when one of the rockets fell in the city's central market. Three people were hit by shrapnel from the rocket, and four others were suffering from shock. Three of the wounded were evacuated to Barzilai Hospital in Ashkelon. On Friday, in the Askar refugee camp near Nablus, IDF troops shot and killed Tamr Kandil, a senior member of Fatah's military wing, the Aksa Martyrs Brigades. Kandil, 22, had been involved in several attempts to dispatch suicide bombers into Israel, as well as several shooting attacks in the area. AP contributed to the report.