The abduction of the officer, 2nd Lt. Hadar Goldin, 23, brought to an end after just 90 minutes a promised 72-hour cease-fire, as Israel responded to what it said was a clear violation of the terms of the truce.
In a statement early Saturday morning, the military wing of Hamas said it had no knowledge of Goldin's whereabouts and suggested that he may have been killed by the Israeli airstrikes that followed the apparent abduction.
"We have lost contact with the group of fighters that took part in the ambush and we believe they were all killed in the [Israeli] bombardment," the statement said. "Assuming that they managed to seize the soldier during combat, we assess that he was also killed in the incident."
A senior Israeli official acknowledged it was possible that Goldin had been killed but said Israel had seen "nothing conclusive."
"His kidnapping happened in the framework of a deadly attack in which two others were killed. We know that it's possible he's dead," said the official, who spoke on the condition of anonymity because of the sensitivity of the situation. "Having said that, our operational assumption is that he's alive, and we're looking for him."
Goldin was abducted when his unit, which was preparing to destroy a tunnel between Gaza and Israel, was ambushed by Palestinian militants, including a suicide bomber. Two Israeli soldiers were killed, and Goldin was apparently pushed back through the tunnel.
Hamas insists the incident occurred before the cease-fire took hold and that it was Israel that broke the terms of the truce.
If Goldin is alive and in Hamas's custody, it could alter the course of the conflict. The last Israeli soldier to be captured and held in Gaza, Gilad Shalit, was not released for five years. Shalit was ultimately traded for 1,100 Palestinian prisoners.
Israel's security cabinet met deep into Friday night — a highly unusual development on the Jewish Sabbath. But no announcements followed, and Israeli officials declined to comment on what may have been decided.
In a sign of how little hope exists for a diplomatic breakthrough to end the conflict after 26 days, Israel said Saturday it would not attend negotiations planned for Sunday in Cairo. Foreign Ministry spokesman Paul Hirschson said the talks had been scheduled as part of the cease-fire deal but that the deal had been voided by Hamas.
"When there's a credible proposal, we'll listen," he said. "But there's a certain skepticism about whether these guys have any interest in a cease-fire."
Hamas spokesman Sami Abu Zuhri said Palestinian factions, including Hamas, would attend the talks but that delegates from Gaza would not be among them because of security concerns.
Egyptian President Abdel-Fattah el-Sissi suggested the talks would go forward, saying that Egypt's proposal represented "the real chance to find a solution to the crisis in Gaza and to end the bloodshed."
Israel's bombardment of Gaza continued Saturday, with fire focused on the Rafah area where Goldin disappeared. At least 35 Palestinians were killed overnight in addition to the 52 who died on Friday, according to Gaza Health Ministry officials. Some 450 people were injured.
Palestinian officials said that several mosques and the Islamic University in Gaza City were among the targets of the overnight airstrikes.
Israel said late Saturday morning that it had attacked 200 sites within the past 24 hours, and that the university site and the mosques that had been targeted were being used to develop and store weapons.
Residents of the town of Beit Lahiya in the northern Gaza Strip were told Saturday afternoon that they could return to their homes because Israel's operations in those areas had ended. But Israeli officials said the announcement did not reflect any broader de-escalation of the conflict.
Since the fighting began on July 8, at least 1,650 Palestinians have been killed and more than 8,900 injured, Gaza officials say. Sixty-three Israeli soldiers have been killed and more than 400 wounded. Three civilians have been killed by mortar rounds or rockets fired by militants from Gaza into Israel.
That fire continued Saturday morning, with at least 10 rockets fired toward Israel by noon and Israel's Iron Dome defense system intercepting two that were headed toward Tel Aviv.
President Barack Obama, speaking in the White House briefing room Friday, urged Hamas and other Palestinian factions to release Goldin, saying that was an essential condition for a durable truce. He added that Israel had "a right to defend itself."
"I think it's going to be very hard to put a cease-fire together again if Israel and the international community can't feel confident that Hamas can follow through," Obama said. "When they sign on a cease-fire they're claiming to speak for all Palestinian factions. . . . If they don't have control of them . . . then it's hard for the Israelis to feel confident that a cease-fire can actually be honored."
Israel said the capture took place an hour and a half after the truce began Friday morning. It said the officer was taken in the no man's land in the seaside enclave, east of Rafah. Hamas officials said the clashes occurred before the truce began.
Both sides accused each other on Friday of breaking the cease-fire. Sami Abu Zuhri, a Hamas spokesman, declared that Israel was misleading the world to justify "its violation of the truce and to cover up their savage massacres in Rafah."
Israeli Prime Minister Benjamin Netanyahu told Secretary of State John Kerry in a telephone call Friday afternoon that the cease-fire was broken by Hamas and that the Islamist group and other Palestinian militant factions "will bear the consequences of their actions," according to Netanyahu's office.
In a statement issued after his phone conversation with Netanyahu, Kerry reproached Hamas for breaking assurances given to the United States and the United Nations. He called on Hamas to release the captive immediately and unconditionally. "It would be a tragedy if this outrageous attack leads to more suffering and loss of life on both sides of this conflict," he said.
While Qatar and Turkey played a role in confirming Hamas's agreement to honor a cease-fire, the United Nations also had "assurances we had received directly" from the Hamas leadership, U.N. Undersecretary Jeffrey Feltman said Friday.
Saying that the United Nations was "profoundly disappointed" that the lull in fighting "seems to have lasted for maybe 90 minutes this morning," Feltman described it as a "tragic loss of opportunity for both sides."
The 72-hour cease-fire had been designed not only to allow humanitarian relief for both sides but also to pave the way for a durable truce through the discussion of demands from both sides in Cairo.
"I hope we can get back to that," Feltman said. "But it's going to be extremely difficult in the situation that we see in the Gaza Strip now, particularly with the captured Israeli soldier."
On Friday morning, after the truce began at 8 a.m. local time, Gazans emerged from their homes to shop or visit families. Others went back to their neighborhoods to assess the damage to their houses, retrieve belongings and bury their dead. Fishermen jumped into their boats and headed to sea while children played on the beach and frolicked in the waves.
By midday, as the news spread of the collapse of the truce, they fled back to their homes and the streets were once again empty.
Israeli analysts said Netanyahu and his top advisers will have to consider expanding the operation in Gaza — even if that was not their original intent.
"It puts the cabinet in a very awkward position," said Meir Elran, a former deputy director of military intelligence and current researcher at the Institute for National Security Studies in Tel Aviv. "So far the idea was to do away with the tunnels and extract ourselves from Gaza. But there are a lot of calls within Israel to expand the pressure."
Elran said that could take the form of a much more aggressive ground operation, which he described as "very, very limited" until now.
Shaul Shay, a former deputy head of Israel's National Security Council, said Goldin's abduction represented a major success for Hamas, becoming a source of leverage, both in crafting a truce and negotiating an exchange for the release of Hamas members held in Israeli jails.
"From their point of view, it's a significant achievement — maybe their most significant achievement in this conflict," said Shay, a senior research fellow at the Begin-Sadat Center for Strategic Studies.
He said that rescuing Goldin, if he is still alive, will inevitably force Israel to shift its focus and direct energies toward finding the missing soldier, prolonging a war that has already stretched longer than Israel's two other major conflicts in Gaza against Hamas, in 2008-2009 and 2012.
There's little guarantee, though, that Goldin can be found and brought out alive. "It's not a simple task. We've seen how they use tunnels, and it's a built-up area," Shay said.
"This morning we had a 72-hour cease-fire," he added. "Now we're in a situation where Israel has to continue its operation until this soldier is found."
Witte reported from Jerusalem. Washington Post staffers Karen DeYoung in Washington, Ruth Eglash in Jerusalem and Islam Abdel Karim in Gaza City contributed to this report.
