The U.N. Security Council condemned the escalation of violence following Israel's attack on the office of the prime minister of Hamas-ruled Gaza.
The Council adjourned its emergency session early Sunday and issued a statement that calls for all parties to respect their obligations under international law.
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U.N. Secretary-General Ban Ki-moon said he recognized Israel's right to defend itself but accused Israel of "disproportionate and excessive use of force."
Israeli aircraft sent missiles slamming into Prime Minister Ismail Haniyeh's office in Gaza before dawn on Sunday, pressing forward with an offensive that has killed nearly 70 Palestinians in two days of fighting. A 21-month-old girl was among the dead in new violence.
Haniyeh's office was empty at the time of Sunday's airstrike, but the raid was seen as a tough message to the Hamas leadership, which Israel holds responsible for repeated rocket barrages launched from Gaza.
A total of 54 Palestinians, roughly half of them civilians, were killed in fighting Saturday, the highest single-day death toll in more than seven years of violence. Two Israeli soldiers also were killed.
Responding to the bloodletting, the moderate Palestinian leadership based in the West Bank suspended U.S.-sponsored peace talks with Israel. Secretary of State Condoleezza Rice is due to arrive this week, but instead of promoting peace talks, she likely will try to put out the latest fire.
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Israeli Prime Minister Ehud Olmert on Sunday rejected the international criticism and vowed to continue the Gaza offensive. "With all due respect, nothing will prevent us from continuing operations to protect our citizens," he told his Cabinet.
Olmert's defense minister, Ehud Barak, said an even broader Gaza operation was in the cards, aimed at crushing militant rocket squads but also to "weaken the Hamas rule, in the right circumstances, even to bring it down."
Israel regularly clashes with Gaza rocket squads, but intensified its operations after militants fired salvos last week into Ashkelon, a city of 120,000. By targeting Ashkelon, some 11 miles north of Gaza, Hamas added pressure on Israeli leaders to exact a high price for the increasing sense of insecurity felt in southern Israel.
Haniyeh's office was just one of about a dozen targets Israeli aircraft and ground troops struck before dawn.
Overnight, a 14-year-old Palestinian girl and five militants died of their wounds, and four Palestinians were killed in Israeli raids, including the baby girl, who died from shrapnel wounds.
The bodies of two women also were unearthed from the rubble of an earlier Israeli airstrike, bringing the total death toll from the operation to 66 since late Friday.
At least half were militants. Gaza health officials said about 200 people were wounded, 14 critically.
The normally bustling streets of Gaza City, the coastal strip's largest town, were eerily empty Sunday.
Schools and universities were closed. The sound of verses from the Muslim holy book, the Quran, pouring forth from mosque loudspeakers mingled with the roar of Israeli warplanes and unmanned drones in the sky. Hamas blocked off roads to government buildings and security installations to protect civilians from possible Israeli strikes.
Hundreds gathered outside hospitals in Gaza City and northern Gaza waiting for bodies to be brought forth from morgues for burial. Many, like schoolteacher Tawfek Shaban, a 44-year-old father of five, were holding small radios, listening to the news.
"Shame on the Arabs, shame on the Muslims, shame on humanity ... When they will act to stop Israel?" Shaban asked. "There is no safe place in Gaza."
The Israeli onslaught failed to stop rockets from battering southern Israel. Nine were fired at southern Israel by midday Sunday, including one that struck a house in the rocket-scarred town of Sderot, the military said. No one was injured. About 50 rockets and mortars were fired Saturday, wounding six Israelis.
"The Zionists will not enjoy security in ... all the colonies around Gaza as long as their crimes continue," said Abu Obeida, a spokesman for Hamas' military wing.
The Saturday toll was by far the highest since the second Palestinian uprising erupted in late 2000. The highest previous Palestinian death toll was 38 in March 2002.
The moderate Palestinian leadership in the West Bank, which is locked in a fierce rivalry with Hamas, called Israel's assault a "holocaust" and "genocide" and suspended peace talks.
"For the time being, the negotiations are suspended because we have so many funerals," Palestinian negotiator Saeb Erekat said Sunday. It was unclear when the talks, relaunched last November at a U.S.-hosted summit, would resume.
But Olmert said "attacking Hamas strengthens the chance for peace."
"I'm sure that beyond certain statements, the Palestinian leadership, the one with whom we want to achieve peace, also understands that," he said.
Olmert and the moderate Palestinian president, Mahmoud Abbas, have set a year-end target for reaching an accord.
Abbas has ruled from the West Bank since his Hamas rivals violently seized control of Gaza last June. But the deaths of Palestinians in Gaza has threatened to unleash a backlash against him in the West Bank.
In Ramallah, home to Abbas' government, thousands of schoolchildren demonstrated against Israel. Some accused Abbas of being an Israeli agent, and protesters threw stones and cars, burned tires and forced shopkeepers to close their stores.
And in the West Bank city of Hebron, several hundred Palestinian youths threw stones and bottles at an Israeli checkpoint in the city center. Israeli troops responded with rubber bullets and gas, slightly wounding two people.