A three-day Gaza cease-fire that began Friday quickly unraveled, with Israel and Hamas accusing each other of violating the truce amid new fighting.

A day that was supposed to have marked a tentative first step toward peace between Israelis and Palestinians instead signaled a precipitous slide back into full-on warfare.

A hard-won truce collapsed within two hours Friday after the Israeli military said one of its soldiers was missing and two were dead amid heavy fighting against Palestinian militants in the southern Gaza Strip. The apparent capture, a nightmare scenario for Israelis, could vastly complicate any new cease-fire push.

Israeli Prime Minister Benjamin Netanyahu accused Hamas, the militant group that controls Gaza, of “flagrantly violating” what was to have been a three-day humanitarian pause in fighting that has killed nearly 1,500 Palestinians and at least 63 Israeli troops over the last 31/2 weeks.

Hamas insisted that the clash in Rafah, at Gaza’s southern tip, had occurred before the start of the aborted cease-fire.

The U.S. government accepted Israel’s version of events and condemned Hamas. The quick breakdown of the truce appeared to have moved the U.S. and Israel closer after a week of strained relations.

President Obama said at a White House news conference that arranging a halt to the fighting in Gaza “will take some time.”

“It's going to be very hard to put a cease-fire back together if the Israelis and the international community can't feel confident Hamas can follow through on a cease-fire commitment,” he said.

Israelis were “entirely right” to try to dismantle the militant group’s network of tunnels leading from Gaza into Israel, he said, but added that “there is a way of doing that while still reducing the bloodshed.”

The 72-hour break in fighting had been announced with considerable fanfare hours earlier by Secretary of State John F. Kerry and United Nations Secretary-General Ban Ki-moon, capping more than two weeks of frustrated efforts to stem the bloodshed.

Anger about the continuing violence again boiled over into the West Bank, where two Palestinians died in clashes with Israeli forces, reigniting the specter of a widening conflict outside Hamas-run areas.

After the Israeli soldier went missing, troops pushed deep into Rafah, essentially dividing it into sectors as they sought the man, identified as 2nd Lt. Hadar Goldin. Palestinian officials said at least 60 people died as tank shells and airstrikes raked ramshackle neighborhoods that offered little cover to fleeing civilians. Hospitals and clinics were swiftly overwhelmed with dead and wounded.

Historically, Israelis have regarded the seizing of their troops by enemies as akin to a family tragedy, and public opinion has supported dramatic measures to win the captives’ freedom, such as the massive prisoner swap that resulted in the release of Gilad Shalit, held five years in Gaza by Hamas.

Netanyahu’s government is unlikely to make any significant concessions to the militant group while the soldier’s fate is still unknown. Islamic militants previously have used soldiers’ remains as macabre bargaining chips.

Fighting between the two sides continued almost until the last minute before the lull that took effect at 8 a.m. Overnight, airstrikes had pounded eastern and northern Gaza, close to the fence surrounding the enclave, and rocket fire continued throughout the night.

But soon after daybreak — with word of the latest truce having spread even among those without television or electricity — Palestinians quickly seized upon the respite, trekking to devastated neighborhoods that had been no-go zones because of heavy bombardment. Fishermen put out to sea in their small boats, slipping out of Gaza City’s harbor for the first time in days.

Hamas police officers, out of sight for three weeks, took up traffic duties, directing the cars and donkey carts that quickly formed bottlenecks on major arteries in Gaza City. And, as always, there were dead to be buried and injured who needed care.

Wafi Jamal Sheik ventured into a ruined neighborhood in eastern Gaza, hoping his house might still be standing. “There’s nothing left,” the 30-year-old handyman said. He was carrying a plastic-wrapped bundle containing a few cups and plates salvaged from what had been the kitchen.

Israeli military spokesman Lt. Col. Peter Lerner said the Rafah confrontation came as Israeli forces were trying to destroy an infiltration tunnel, as allowed under the cease-fire terms. They were attacked by suspected Hamas militants whose ranks included a suicide bomber, he said, and in the chaos a man went missing — dragged into the tunnel, Israel feared.

Meanwhile, militants fired barrages of rockets and mortar rounds into Israel, apparently seeking to prove they could still send Israelis scrambling for bomb shelters, even though experts estimate their weapons stockpile has been substantially diminished.

The rapidly mounting Palestinian death toll, together with the smashing of Gaza’s already crumbling infrastructure and the displacement of nearly a quarter of a million people in the enclave, had spurred mediators led by the United States and the U.N. to finally push through the truce deal.

Under the accord, both sides received some of the incentives they had demanded: Israel was moving ahead with the destruction of Palestinian tunnels; Hamas was to be part of the Palestinian delegation traveling to talks in Cairo, which would also include the Palestinian Authority and the militant group Islamic Jihad.

But Friday’s events illustrated the fragility of even a brief hiatus in the fighting.

Whereas Hamas and Islamic Jihad swiftly announced their willingness to abide by the truce as long as Israel did, Netanyahu’s government waited until just a few hours before the cease-fire took effect to formally confirm it. The Israeli leader had asserted repeatedly before the truce announcement that Israel would not accept terms that precluded continuing operations to destroy the tunnels.

Times staff writer King reported from Gaza City and special correspondent Sobelman from Jerusalem. Times staff writer Paul Richter in Washington contributed to this report.

Twitter: @LauraKingLAT