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Hatem Moussa, Associated Press
Palestinian carry the body of Zuhair al-Qaissi, commander of the armed wing of the Popular Resistance Committees (PRC), during his funeral in Rafah, southern Gaza Strip, Saturday, March 10, 2012. The worst exchange of strikes between Israel and the Gaza Strip so far this year entered its second day on Saturday, as Israeli aircraft carried out raids that have so far killed 14 militants according to a Palestinian count, and militants responded with nearly 100 rockets.

GAZA CITY, Gaza Strip — Israeli airstrikes killed a 12-year-old boy and a militant in the Gaza Strip early Sunday and Gaza rocket squads fired salvos into southern Israel, officials said, deepening the worst round of violence between the sides in more than a year.

The Israeli military said its aircraft targeted rocket launchers and Gaza health official Adham Abu Salmia confirmed witness reports of the Palestinian dead, as the exchanges of fire entered their third day and Egyptian efforts to achieve a cease-fire faltered.

"There is no room to talk about the calm considering the continued Zionist aggression on Gaza," Khaled Batch, a leader of the Islamic Jihad militant faction in Gaza, told The Associated Press.

Israeli police spokesman Micky Rosenfeld said the rockets launched from Gaza caused no injuries or damage. The military claims more casualties were averted because Iron Dome missile defense batteries intercepted 90 percent of the rockets they targeted.

Israeli airstrikes have killed 17 Gazans and Gaza militants have fired more than 110 rockets at Israel, seriously wounding a civilian, since the clashes erupted Friday with an Israeli air assault that killed the commander of a militant group.

Israel accused Zuhair al-Qaissi of plotting an infiltration attack into Israel from Egypt's lawless Sinai peninsula, similar to the one they claim he orchestrated in August, which killed eight Israelis. His militant group, the Hamas-allied Popular Resistance Committees, has never taken responsibility for that raid.

Some 1 million Israelis are within range of rocket fire from Gaza, and on Sunday, schools throughout the area and Ben-Gurion University in Beer Sheva were closed because of the fighting. Rosenfeld said police stepped up their presence in southern Israel.

Israel and Gaza militants have frequently traded low-level fire since the 2009 war, but a flare-up of this intensity is rare. The United Nations and the U.S. State Department have condemned the violence and called on both sides to exercise restraint.

Gaza's militant Islamic Hamas rulers have denounced the Israeli airstrikes but their fighters have not attacked Israel, leaving that to other smaller Palestinian militant groups.

Hamas has largely avoided direct attacks on Israel since the Jewish state conducted a bruising three-week war against the militant group in early 2009 that killed hundreds of Gazans and destroyed many Hamas facilities. But the Iranian-backed militant group has been smuggling increasingly sophisticated weapons into the seaside territory and Israel holds it responsible for all violence emanating from Gaza.

Israeli Foreign Minister Avigdor Lieberman told Israel Radio on Sunday that there was no point in Israel's launching another large-scale offensive in Gaza unless it sets out to topple the Hamas regime. Lieberman wouldn't say whether such an operation was planned but noted that the violence from Gaza was "unacceptable and we won't reconcile ourselves to it."

Despite Lieberman's tough talk, neither side is believed to be interested in all-out war.

Egypt, which has helped arrange truces in the past, has been trying to arrange a cease-fire, but an official there said the Egyptians were encountering resistance from two militant grouops, al-Qaissi's PRC and Islamic Jihad. Both factions want guarantees that Israel won't target their groups, he said, but that is something said Egypt cannot deliver.

The Egyptian official spoke on condition of anonymity because he was not at liberty to divulge details of cease-fire efforts.