TEL AVIV, Israel -- Fighting between militants in Gaza and the Israeli military intensified Tuesday, clouding the prospects of a durable cease-fire, as Secretary of State Hillary Rodham Clinton rushed to the region to try to prevent a major escalation of the conflict.
Israeli officials and negotiators from the militant group Hamas, communicating through Egyptian interlocutors, remained at odds late Tuesday over details of the truce that the international community furiously was trying to broker. Among the main sticking points was whether Egypt and the United States could act as dependable guarantors of a peace deal in a region where waves of aggression have come in vicious cycles.
A former senior Israeli official who has been briefed on the negotiations said both sides have indicated that they prefer a cease-fire to avert an Israeli ground invasion, which could multiply casualties and spark a broader regional conflagration. But neither wants to back down without getting significant concessions, said the former official, who spoke on condition of anonymity to discuss private negotiations.
The Israelis, the former official said, want a commitment that Egypt will do a better job of policing its porous border with Gaza, which includes dozens of tunnels used to smuggle everything from vehicles to parts for long-range rockets into the territory. Hamas, which rules the Gaza Strip, wants Israel to lift its blockade of the enclave, home to 1.7 million Palestinians.
Putting to rest rumors and assertions throughout the day that suggested a cease-fire deal was imminent, Israeli Prime Minister Benjamin Netanyahu made clear to Ms. Clinton that he has not ruled out a ground invasion.
"If there is a possibility of achieving a long-term solution to this problem through diplomatic means, we prefer that," he said. "If not, I'm sure you understand that Israel will have to take whatever action is necessary to defend its people. This is something I don't have to explain to Americans."
The impasse was a blow to Egyptian President Mohamed Morsi, who had said earlier Tuesday that he expected a deal within hours. The Israeli military said Gaza militants launched 200 rockets Tuesday, while Israel struck more than 133 targets in Gaza.
Ms. Clinton, looking weary after flying across five time zones from Cambodia, where she had been attending a regional summit with President Barack Obama, spoke firmly about her desire to avert greater bloodshed. "America's commitment to Israel's security is rock-solid and unwavering," she said late Tuesday before sitting down with Mr. Netanyahu. "That is why we believe it is essential to de-escalate the situation in Gaza."
The former Israeli official briefed on the discussions said a key concern is clearly defining the role that Egypt would play as a guarantor if a deal were reached. "The cessation of smuggling requires a strong Egyptian role," the former official said. "I don't believe Hamas will commit to halt smuggling weapons."
Israel also wants the deal to include establishment of a buffer zone along its border with Gaza to prevent attacks on Israeli patrols, the former official said.
Hamas has demanded the permanent lifting of the Gaza blockade, the former official said, a concession Israel is unlikely to grant. Israel says the measure is designed to keep militants from smuggling weapons and building bunkers.
Complicating matters, the former official said, the Egyptians are making demands of their own. Cairo wants Hamas to rein in Gaza-based militant groups that have formed alliances in recent years with extremists in Egypt's Sinai Peninsula.
Tuesday was among the most violent days since Israel's operation, called Pillar of Defense, began a week ago. The campaign seeks to cripple militant cells in Gaza that have stockpiled enormous caches of rockets that are routinely fired toward southern Israeli towns.
The Israeli military suffered its first casualty of the offensive Tuesday, when an 18-year-old corporal was killed by a rocket in southern Israel. Five other Israeli soldiers were wounded by artillery Tuesday, the military said. A civilian Israeli defense employee was killed in a separate rocket attack in southern Israel, officials said, raising the Israeli death toll to five.
More than 130 Palestinians have been killed in Gaza since the fighting began, according to health officials.
In Gaza City, meanwhile, masked Hamas gunmen publicly executed six alleged Israeli spies at a large intersection, the Associated Press reported. Hamas' military wing accused the men of giving Israel information about fighters and rocket-launching sites. The suspects were forced to lie facedown in the street and shot, and one of the corpses was tied to a motorcycle and dragged through the streets as passersby screamed, "Spy! Spy!"
In a surprise visit Tuesday to Israel, U.N. Secretary-General Ban Ki-moon appealed for an end to hostilities.