JERURUSALEM — 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.