3 killed as Israel continues strikes on Gaza (CBS/AP) GAZA CITY, Gaza Strip - Israeli air strikes killed two Palestinian militants and a schoolboy in the Gaza Strip this Monday as Palestinian rocket squads barraged southern Israel, in escalating fighting that has defied international truce efforts. The cross-border violence, touched off by Israel's killing of a top militant leader on Friday, has been the worst exchange of fire between Israel and the Hamas-ruled territory in months. The fighting has killed 21 Gazans, including 18 militants, seriously wounded two Israelis, and disrupted the lives of 1 million Israelis living in Gaza rocket range. The Israeli military said it carried out nine air attacks against rocket-launching sites and a weapons storage facility early Monday. Islamic Jihad said two of its militants were killed in two separate raids, one while he was riding a motorcycle. A 16-year-old boy wearing a school uniform was killed when a group of five civilians was struck in another attack, Gaza health official Adham Abu Salmia said. Two dozen people, including several children, were wounded in a separate predawn strike in Gaza City, Abu Salmia said. Chief Israeli military spokesman Brig. Gen. Yoav Mordechai told Army Radio that this raid had targeted munitions that were stored in a residential building. The military said the air attacks came in response to continued rocket fire, and Israeli police spokesman Micky Rosenfeld reported that 12 rockets were fired into southern Israel early Monday. CBS Radio News correspondent Robert Berger reports that more than 160 rockets have paralyzed southern Israel since Friday and schools and many businesses are closed. Egypt is trying to a broker a cease-fire, but for now both sides have vowed to keep on fighting. Berger also reports that Palestinian spokesman Abu Mujahid promised revenge: he said "innocent blood will not be spilled in vain" and that armed factions would defend the Palestinian people against Israeli "aggression." Israeli Prime Minister Benjamin Netanyahu at a press conference during his visit to the port city of Ashdod, near the border with the Gaza Strip, March 11, 2012. On the other side, during a visit to southern Israel on Sunday, Prime Minister Benjamin Netanyahu vowed the air strikes would continue as long as necessary. We have a clear policy: we will hit anyone who plans to harm us, who prepares to harm us and who harms us. Israel says the newly introduced Iron Dome missile defense system intercepted dozens of the rockets since the clashes erupted, and military officials speculated this averted more casualties. But although the violence shows no immediate signs of subsiding, both Hamas and Israel seem eager to avoid the kind of all-out war that erupted three years ago. In keeping with its practice since that conflict, Hamas has stayed out of the current clashes, for fear of provoking a harsh Israeli retaliation. But it has not stopped other, smaller Gaza factions from attacking Israel, and Israel continues to hold it ultimately responsible for any violence emanating from Gaza. In the past, similar flare-ups have died out by themselves or with informal cease-fires negotiated by third parties, often Egypt. Egypt has been trying to mediate an end to the clashes, and Hamas has also appealed to other Mideast countries to join the truce attempts. But so far efforts have failed, with militants and Egypt insisting that Israel first halt its air strikes. The Zionist state began this aggression. It has to stop its aggression first and then we will evaluate the situation and study the possibility of calm," the deputy secretary-general of Islamic Jihad, Ziad Nakhleh, was quoted as saying on the movement's web site. Mordechai, the Israeli military spokesman, told Israel Radio that Israel would halt its raids if the rocket fire would cease, but added that the Israeli military would continue to take pre-emptive action to foil militant attack plans. Israel says it launched Friday's initial air strike to stop a militant group's plan to infiltrate into Israel through Egypt's Sinai peninsula. Israel says the group, the Popular Resistance Committees, was behind a similar border raid in August that killed eight Israelis, but the PRC has never acknowledged involvement. Mordechai, the military spokesman, said Monday that Israel was prepared for a ground offensive if necessary. He also said Israeli military chief Lt. Gen. Benny Gantz has postponed a trip this week to the U.S. because of the fighting.