Hours after the main exchange, the Israeli military said troops shot two men seen moving suspiciously toward a frontier "no-go" zone in the north of the coastal enclave.
"An army force spotted two suspects moving toward the border fence and opened fire," a spokeswoman said. "The two were seen to have been hit."
Palestinian officials said Israeli tanks fired several shells into Gaza after dark but they had no reports of casualties.
The armed wing of Gaza's ruling Hamas movement took responsibility for the mortar barrage, three days after an Israeli air strike killed two of its members in Gaza.
The Israeli military said "around 50" mortar bombs fell on or around southern Israeli communities near the border with the Gaza in the biggest violation yet of an informal truce militants confirmed in January.
"In response to this massive fire there was pinpoint fire from tanks and helicopters at several suspect locations," an army spokeswoman told AFP.
She said two Israeli civilians were lightly wounded by the Palestinian shelling.
The Palestinian Ezzedine al-Qassam Brigades said they targeted border crossings of Sofa, Kessufim and Nahal Oz.
Palestinian witnesses said some 10 shells had been fired at Sofa.
A Palestinian emergency services official said a subsequent Israeli air strike wounded five people Saturday in the Gaza City suburb of Zeitun.
Spokesman Adham Abu Selmiya said a child was among those wounded in the attack, which witnesses said targeted a Hamas security base.
Two members of the Ezzedine al-Qassam Brigades were killed on Wednesday in an air strike on what Israel said was a militant training camp in Zeitun.
Witnesses said that in Saturday's exchange the Israelis also hit targets east of Khan Yunis, in southern Gaza, and in the refugee camp of Deir el-Balah in the centre of the territory.
Gaza residents said that the Israeli fire damaged a main electrical cable serving Gaza City and the northern strip, leading to widespread power cuts.
"Prime Minister Benjamin Netanyahu said he regards with gravity the... attacks by Hamas on Israeli residents," a statement from his office said. "Israel will take all necessary means to protect its citizens."
An earlier statement from the office of Foreign Minister Avigdor Lieberman said he had told Israel's UN mission to lodge a complaint about the mortar fire.
It noted the attack came as Palestinian president Mahmud Abbas, whose Fatah movement controls the West Bank, was seeking reconciliation with Hamas.
Saturday's barrage took past 100 the number of projectiles Israel says Gaza-based militants have fired into its territory since the beginning of the year.
Israel routinely responds to the rocket and mortar fire with air raids on Gaza.
It carried out a 22-day offensive, codenamed "Operation Cast Lead" against Gaza rocket fire in December 2008 and January 2009, in which 1,400 Palestinians died, more than half of whom were civilians, and 13 Israelis, 10 of them soldiers.
Opposition Chairwoman Tzipi Livni said that Saturday's hail of mortar fire meant the time had come for a fresh military campaign.
"The right way to deal with it is with force, just like Israel did during and after Operation Cast Lead," news website Ynet quoted her as telling local authority heads in the border region.
In January, Gaza's main militant factions confirmed a year-old truce after weeks of increased rocket fire and spiralling tensions along the border prompted a warning from Arab leaders that Gaza was risking a major new Israeli invasion.
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"An army force spotted two suspects moving toward the border fence and opened fire," a spokeswoman said. "The two were seen to have been hit."
Palestinian officials said Israeli tanks fired several shells into Gaza after dark but they had no reports of casualties.
The armed wing of Gaza's ruling Hamas movement took responsibility for the mortar barrage, three days after an Israeli air strike killed two of its members in Gaza.
The Israeli military said "around 50" mortar bombs fell on or around southern Israeli communities near the border with the Gaza in the biggest violation yet of an informal truce militants confirmed in January.
"In response to this massive fire there was pinpoint fire from tanks and helicopters at several suspect locations," an army spokeswoman told AFP.
She said two Israeli civilians were lightly wounded by the Palestinian shelling.
The Palestinian Ezzedine al-Qassam Brigades said they targeted border crossings of Sofa, Kessufim and Nahal Oz.
Palestinian witnesses said some 10 shells had been fired at Sofa.
A Palestinian emergency services official said a subsequent Israeli air strike wounded five people Saturday in the Gaza City suburb of Zeitun.
Spokesman Adham Abu Selmiya said a child was among those wounded in the attack, which witnesses said targeted a Hamas security base.
Two members of the Ezzedine al-Qassam Brigades were killed on Wednesday in an air strike on what Israel said was a militant training camp in Zeitun.
Witnesses said that in Saturday's exchange the Israelis also hit targets east of Khan Yunis, in southern Gaza, and in the refugee camp of Deir el-Balah in the centre of the territory.
Gaza residents said that the Israeli fire damaged a main electrical cable serving Gaza City and the northern strip, leading to widespread power cuts.
"Prime Minister Benjamin Netanyahu said he regards with gravity the... attacks by Hamas on Israeli residents," a statement from his office said. "Israel will take all necessary means to protect its citizens."
An earlier statement from the office of Foreign Minister Avigdor Lieberman said he had told Israel's UN mission to lodge a complaint about the mortar fire.
It noted the attack came as Palestinian president Mahmud Abbas, whose Fatah movement controls the West Bank, was seeking reconciliation with Hamas.
Saturday's barrage took past 100 the number of projectiles Israel says Gaza-based militants have fired into its territory since the beginning of the year.
Israel routinely responds to the rocket and mortar fire with air raids on Gaza.
It carried out a 22-day offensive, codenamed "Operation Cast Lead" against Gaza rocket fire in December 2008 and January 2009, in which 1,400 Palestinians died, more than half of whom were civilians, and 13 Israelis, 10 of them soldiers.
Opposition Chairwoman Tzipi Livni said that Saturday's hail of mortar fire meant the time had come for a fresh military campaign.
"The right way to deal with it is with force, just like Israel did during and after Operation Cast Lead," news website Ynet quoted her as telling local authority heads in the border region.
In January, Gaza's main militant factions confirmed a year-old truce after weeks of increased rocket fire and spiralling tensions along the border prompted a warning from Arab leaders that Gaza was risking a major new Israeli invasion.
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