JERUSALEM » Israel-Hamas fighting looked headed for escalation after U.S. Secretary of State John Kerry failed Friday to broker a weeklong truce as a first step toward a broader deal and Israel’s defense minister warned Israel might soon expand its Gaza ground operation "significantly."

Hours after the U.S.-led efforts stalled, the two sides agreed to a 12-hour humanitarian cease-fire to begin Saturday. However, the temporary lull was unlikely to change the trajectory of the current hostilities amid ominous signs that the Gaza war is spilling over into the West Bank.

In a "Day of Rage," Palestinians across the territory, which had been relatively calm for years, staged protests against Israel’s Gaza operation and the rising casualty toll there. In the West Bank, at least six Palestinians were killed by Israeli fire, hospital officials said.

The latest diplomatic setbacks, after several days of high-level diplomacy in the region, signaled that both sides are digging in and that the fighting in Gaza is likely to drag on.

Israel wants more time to destroy Hamas military tunnels and rocket launching sites in Gaza, while the territory’s Hamas rulers want international guarantees that a Gaza border blockade will be lifted before they cease fire.

The Israeli military said in a statement that Saturday’s 12-hour pause in fighting would start at 8 a.m. But it warned that the military "shall respond if terrorists choose to exploit" the lull to attack Israeli troops "or fire at Israeli civilians." The military also said that "operational activities to locate and neutralize tunnels in the Gaza Strip will continue."

A Hamas spokesman, Sami Abu Zuhri, said earlier Friday that the group had agreed to the 12-hour lull, intended to allow civilians to receive aid and evacuate to safer areas.

Civilians on both sides have been hardest hit over the past 18 days.

In Gaza, Israeli airstrikes and tank shelling have killed more than 860 Palestinians, wounded more than 5,700, displaced tens of thousands and destroyed hundreds of homes, Palestinian officials said. In dozens of cases, Israeli attacks killed three or more members of the same family, according to U.N. figures, and civilians make up three-quarters of the dead.

Gaza militants have fired close to 2,500 rockets at Israel since July 8, exposing most of Israel’s population to an indiscriminate threat that has killed three civilians. Thirty-six soldiers have also been killed in battle in Gaza.

Israeli Defense Minister Moshe Yaalon said Friday that Israel’s military would continue to strike Hamas hard, in order to deter it from firing rockets at Israel in the future.

"At the end of the operation, Hamas will have to think very hard if it is worth it to taunt us in the future," Yaalon was quoted as telling soldiers manning an Iron Dome anti-missile battery. "You need to be ready for the possibility that very soon we will order the military to significantly broaden ground activity in Gaza."

"Hamas is paying a very heavy price and will pay an even heavier price," he said, according to a statement by his office.

The warning came shortly after Kerry announced in Cairo that he had been unable to broker a weeklong truce during which both sides were to talk about security arrangements and a possible easing of Gaza’s border blockade.

For days, Kerry had been moving between the Egyptian capital, the West Bank and Jerusalem, and talking to officials from Qatar, who are in contact with Hamas. More meetings with his counterparts from European Union nations, Turkey and Qatar were scheduled for Saturday in France.

Speaking alongside U.N. chief Ban Ki-moon and the Egyptian foreign minister, Kerry insisted there was a general agreement on the "concept" of a truce but that both sides had concerns over details of carrying it out.

"Gaps have been significantly narrowed," he said. "It can be achieved, if we work through some of the issues that are important for the parties."

However, the Israeli Security Cabinet rejected Kerry’s proposal, according to Israeli media reports. Israel wants to be able to continue destroying tunnels used by Hamas militants to try to infiltrate into Israel and to smuggle weapons. It has so far uncovered 31 tunnels and destroyed half of them.

Meanwhile, heavy Israeli shelling was reported in the town of Beit Hanoun in the northern Gaza Strip, an area where ground troops are operating.

One shell hit near the emergency department of Beit Hanoun hospital, wounding six people, including a foreign national who was not identified further, the Red Crescent said. Two of the wounded were in critical condition.

Shells also hit an ambulance in Beit Hanoun, killing a paramedic and wounding two people, the Red Crescent said. Another ambulance driver was killed as he tried to evacuate wounded from the southern town of Bani Suheila, the organization said.

As the Gaza fighting dragged on, the West Bank was becoming increasingly restive, with protests erupting Friday across the territory.

In the northern village of Hawara, hundreds took part in a protest after emerging from a mosque after Friday prayers, said Mayor Mouin Idmeidi. Hawara is located along a main north-south thoroughfare that is also used by Israeli motorists, and one Israeli driver slowed down as he passed the march and fired at the group, the mayor said.

He said four people were wounded and that one of them, a 19-year-old, died at Rafidiyeh Hospital in Nablus of his injuries.

After the shooting, clashes erupted between Palestinians and Israeli troops who opened fire, killing a 22-year-old, Idmeidi said. Health workers at the hospital confirmed the deaths.

An Israeli police spokesman, Mickey Rosenfeld, said paramilitary border police opened fire to disperse violent protests at Hawara, and that masked Palestinians threw firebombs. He said he was unaware of a shooting involving an Israeli civilian.

In Beit Omar, clashes erupted between Israeli forces and Palestinian stone-throwers. Hebron hospital officials said three Palestinians were killed.

Later Friday, the Israeli military said a soldier opened fire and killed a Palestinian protester who attempted to snatch his weapon during clashes in a refugee camp near the city of Hebron. Palestinian police said the man was killed after scuffling with a soldier who had barred him from entering his home before the break of the Ramadan fast.

On Thursday, thousands of Palestinians clashes with Israeli forces at a West Bank checkpoint and in east Jerusalem, the largest protests in those areas in several years.

Associated Press writers Mohammed Daraghmeh in the West Bank, Yousur Alhlou in Jerusalem and Edith M. Lederer at the United Nations contributed to this report.