OC Southern Command Maj.-Gen. Yoav Galant decided Wednesday to extend the deadline for the IDF probe into the cause of Monday's explosion in northern Gaza that killed a mother and her four children. Galant granted more time to the officer leading the investigation, Col. Shai Alkilai, after his initial investigation failed to reach conclusive findings. On Monday morning in the northern Gaza town of Beit Hanun, according to Palestinians, an IDF tank shell hit the Abu Meatak home as the mother, Miyasar, was preparing breakfast for her children. She and four of her children were killed. Following an initial inquiry conducted by the Gaza Division on Monday, the IDF released a statement saying an Israeli aircraft fired a missile at two terrorists next to the home and set off bombs they were carrying, causing a secondary explosion that destroyed the home and killed the Abu Meataks. Alkilai has questioned all of the units that operated in the Beit Hanun area on Monday morning to check whether a tank shell hit the home. Officials said that he was also looking into whether IDF commanders took into account the possibility that the terrorist duo was carrying large bombs - that could cause damage to nearby homes - when the decision was made to target them from the air. The Palestinian-rights group B'tselem on Wednesday called for a criminal probe into the deaths of the Abu Meatak family, saying the IDF appears to have violated international law by firing the missile close to the family's home, despite the high risk of harming civilians. B'tselem said firing a missile close to a home would violate the rule of proportionality set by international law. "In these circumstances, it's highly likely civilians would be at home and be hit by the blast," said Sarit Michaeli, a spokeswoman for B'tselem. "Even if you attack a legitimate military target, the anticipated damage has to be in proportion to the anticipated gain." B'tselem said its investigation showed that four Hamas gunmen were moving in the area at the time, after having earlier that morning fired at IDF soldiers closer to the border with Israel. An IAF missile wounded three of the armed men and a local resident, B'tselem said. Citing witness testimony, B'tselem said a second missile then struck the remaining gunmen, who stood about 15 meters away from the group, and close to the gate of the Abu Meatak courtyard. B'tselem said it believed the second missile killed that gunman and the Abu Meataks. Two older children were critically wounded. B'tselem says testimony it collected raised doubt about the military's claim that the family was killed by a secondary explosion of weapons carried by the gunmen. It noted that a launcher and two rocket-propelled grenades were found later - unexploded - at the scene. It provided a picture of what it said where the weapons. Diaa Halaby, spokesman for the nearby Al-Awda Hospital, told The Associated Press that Myasar Abu Meatak, the dead gunman and one of the wounded gunmen all had the same wounds - shrapnel hits all over the body and shredding of the flesh below the knees. Halaby said such wounds were typical in missile strikes. Robbie Sabel, a lecturer in international law at the Hebrew University, said the case was not clear-cut. He noted that a gunman next to a house did not have immunity. "The rule is that one must try to prevent disproportionate civilian casualties when attacking a military target," he said. "The question in each case is what is disproportionate, and there's no mathematical answer. You have to value the importance of both the military target and the number of civilian casualties."