"What I saw today in the hospital, the wounded and the martyrs, the boy ... whose blood is still on my hands and clothes, is something that we cannot keep silent about," he said.
Israel said it halted its incessant air attacks on militant targets in Gaza during Kandil's visit, though Hamas security claimed three airstrikes hit the territory during that period.
Militants, meanwhile, fired off more than 60 rockets after Kandil arrived in Gaza. The pace of cross-border fighting quickly resumed after the Egyptian leader's departure.
In Egypt's two largest cities, Cairo and Alexandria, thousands protested the Israeli offensive Friday in marches organized by Egyptian President Mohammed Morsi's Muslim Brotherhood. Protesters waved Palestinian flags and chanted slogans against Israel. In Cairo's Tahrir Square, a few hundred protesters burned an Israeli flag.
Prominent Brotherhood figures took part, many brandishing the checkered Palestinian scarf, or keffiyeh, during the marches.
Small anti-Israeli demonstrations occurred in east Jerusalem and the West Bank. Police dispersed the crowds with tear gas and stun grenades. And in Iran, a close Hamas ally, thousands of people took to the streets in the capital Tehran. The demonstrators carried banners denouncing Israel. They chanted "Death to the U.S." and "Death to Israel."
In Europe, reaction was mixed. Germany held Hamas responsible and urged Egypt to pressure the Islamists to halt the violence, while Britain cautioned Israel against launching a ground offensive.
"When Israel has entered into ground invasions in other conflicts that is when they have lost a good deal of international sympathy and support, and of course civilian casualties become much harder to avoid in that situation," Foreign Minister William Hague told reporters in London.
In the West Bank, the Palestinian president, Mahmoud Abbas, announced that U.N. chief Ban Ki-moon would arrive in the region in the coming days in a bid to reduce tensions. Abbas lost control of Gaza to Hamas five years ago but still claims to represent both Palestinian territories. Israeli officials also confirmed Ban was expected. It was not immediately clear whether Ban would visit Gaza.
Israeli Prime Minister Benjamin Netanyahu appeared determined to move forward. "The Israeli military "continues to strike hard against Hamas and is prepared to expand its action into Gaza," he said.
At least 23 Palestinians, including 12 militants and six children, as well as three Israelis have been killed in the fighting — a relatively low toll compared to the beginning of Israel's previous major offensive against Hamas four years ago. Netanyahu has said the air force is trying to strike surgically and avoid harm to civilians.
The 4-year-old boy whose body had been handed to Kandil and Haniyeh was killed along with a young man earlier Friday when an Israeli missile struck close to their homes in the town of Jebaliya near Gaza City, relatives said.
The area near the boy's home showed signs that a projectile had exploded there, with shrapnel marks in the walls of surrounding homes and shattered kitchen windows. But neighbors said security officials quickly took what remained of the projectile, making it impossible to verify who fired it.
Kandil's visit came after a night of fierce exchanges.
Overnight, the military said it targeted about 150 rocket-launching sites as well as ammunition warehouses, bringing to 450 the number of sites struck in the three-day operation.
Militants unleashed dozens of rocket barrages overnight, setting off air-raid sirens throughout an area that is home to some 1 million Israelis.
Early Friday, 85 missiles exploded within 45 minutes in Gaza City, sending black pillars of smoke towering above the coastal strip's largest city. The military said it was targeting underground rocket-launching sites.
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