Israel launched dozens of airstrikes early Saturday in the southern Gaza Strip as part of a large-scale search for a soldier Israel suspects was captured by Hamas fighters.
At least 35 Palestinians were killed in the bombardment and shelling in and around the city of Rafah early Saturday, a Palestinian health official said, adding that the area's main hospital was evacuated because of the strikes.
The Israeli military has said it believes the soldier was grabbed in a Hamas ambush about an hour after an internationally brokered cease-fire took effect Friday morning.
The Hamas military wing on Saturday distanced itself from the soldier's purported capture, which has prompted widespread international condemnation. President Barack Obama and U.N. chief Ban Ki-moon have called for his immediate release.
The Hamas military wing later said in a statement on its website that it is "not aware until this moment of a missing soldier or his whereabouts or the circumstances of his disappearance."
The group said it believes the soldier might have been killed in a clash with Hamas fighters about an hour before the start of the cease-fire.
Hamas said it has lost contact with those fighters and that "we believe all members of this group have died in an (Israeli) strike, including the Zionist soldier the enemy says disappeared."
The Israeli military declined comment on the statement.
The disappearance of the soldier, 2nd Lt. Hadar Goldin, and the heavy clashes that followed it shattered an internationally brokered cease-fire that was to have been in place for three days and open the way for talks in Cairo on a more sustainable truce.
Israel and Hamas have accused each other of violating the humanitarian pause.
The breakdown meant there would be no reprieve for the 1.7 million residents of Gaza, where large parts have been devastated by airstrikes and shelling. More than 1,650 Palestinians — mostly civilians — have been killed and more than 8,000 wounded, according to health official Ashraf al-Kidra.
Israel has lost 63 soldiers and three civilians.
The fighting in Rafah intensified after the disappearance of the soldier and continued Saturday morning, with residents reporting airstrikes along the Egypt-Gaza frontier as well as heavy tank and artillery shelling. The Israeli military said it was searching for the missing soldier and had sent automated calls or text messages to Rafah residents to stay indoors.
"We are under fire, every minute or so tanks fire shells at us," said Rafah resident Ayman Al-Arja. "I have been thinking of leaving since 2 p.m., but tank fire can reach anywhere, and I was scared they will hit my pickup truck. Now we are sitting in the stairwell, 11 members of my family, my brother, his nine children and wife. We just have water to drink and the radio to hear the news."
The 45-year-old Al-Arja added: "We are just staying put waiting for God's mercy."
Since Friday morning, more than 100 Palestinians have been killed in the Rafah area, including 35 early Saturday, al-Kidra said.
The police operations room reported 77 airstrikes on the area and heavy shelling.
The Israeli military said Goldin disappeared in an ambush about an hour after the cease-fire began. Gunmen emerged from one or more Gaza tunnels and opened fire at Israeli soldiers, with at least one of the militants detonating an explosives vest, said Israeli army spokesman Lt. Col. Peter Lerner.
Goldin, a 23-year-old from the central Israeli town of Kfar Saba, was apparently captured in the ensuing mayhem, while another two Israeli soldiers were killed. "We suspect that he has been kidnapped," Lerner said.
Obama called for Goldin's unconditional and immediate release and said it would be difficult to put the cease-fire back together. However, he said the U.S. will continue working toward a cease-fire.
He said Israel committed to the truce, but at the same time called the situation in Gaza "heartbreaking" and repeated calls for Israel to do more to prevent Palestinian civilian casualties.
"Innocent civilians caught in the crossfire have to weigh on our conscience, and we have to do more," Obama said. He added that Israel must be able to defend itself, but that irresponsible actions by Hamas have put civilians in danger.
Israel has gone to great lengths in the past to get back its captured soldiers. In 2011, it traded hundreds of Palestinian prisoners for an Israeli soldier who had been captured by Hamas-allied militants in 2006. The capture of two soldiers in a cross-border operation by Lebanon's Hezbollah guerrillas in 2006 sparked a 34-day war between the Iranian-backed Shiite group and Israel.
Ban blamed Hamas for violating the cease-fire and demanded the immediate and unconditional release of Goldin.
The U.N. chief also urged both sides "to show maximum restraint and return to the agreed 72-hour humanitarian cease-fire," U.N. spokesman Stephane Dujarric said.
Israeli Prime Minister Benjamin Netanyahu told U.S. Secretary of State John Kerry by phone that Palestinian militants had "unilaterally and grossly" violated the cease-fire and attacked Israeli soldiers after 9 a.m.
"Israel will take all necessary steps against those who call for our destruction and perpetrate terrorism against our citizens," Netanyahu told Kerry, according to a statement from the prime minister's office.
Moussa Abu Marzouk, Hamas' deputy leader, denied that Hamas violated the truce. He told Al-Arabiya news channel from Cairo that the movement's military wing carried out no military operations after 8 a.m.
A longtime friend of Goldin said he is engaged to get married and that he studied at a Jewish seminary in the West Bank settlement of Eli. Goldin has a twin brother who also is in the military on the Gaza front lines, said the friend, who spoke on condition of anonymity because he did not have the family's permission to discuss Goldin's personal details with the media.
The soldier's father, Simha Goldin, is a Tel Aviv University professor specializing in Ashkenazi Jewry, the friend said.
"We want to support the military in the fighting against Hamas in Gaza. We are sure the military will not stop before it turns over every stone in Gaza and returns Hadar home safe and sound," the father said in a statement to reporters outside his home.
On Friday, the shelling in Rafah sent families fleeing from apartment blocks. One woman carrying two children rushed toward a parked car, yelling to a bystander, "Quick, open the car door!"
Ambulances ferried the wounded to al-Najar hospital, where family members frantically searched for loved ones among the bloodied bodies on stretchers. Many of the wounded were children. In one room, four children were treated on a single bed, while others were examined on the floor.
On July 8, Israel began an aerial campaign against Gaza aimed at halting Palestinian rocket fire and later sent in ground troops to target launch sites and tunnels used by Hamas to carry out attacks inside Israel.
Four brief humanitarian cease-fires were announced, but each broke within a few hours.
The Israeli military said Gaza militants fired at least 38 rockets and mortars at Israel since the start of Friday's cease-fire, and two were intercepted.
The latest cease-fire, announced by Kerry and Ban, was intended to be the first step toward a lasting truce, with Egypt inviting Israeli and Palestinian delegations to Cairo for talks. Despite its collapse, an Egyptian government official said Cairo had not canceled its invitations. The official spoke on condition of anonymity because he wasn't authorized to talk to the media.
Israel says it has tried to spare civilians by warning them before military strikes, and that Hamas endangers Gazans by firing rockets from residential areas.
Palestinian militants have shot hundreds of rockets into Israel during the conflict, extending their reach to major cities but causing few casualties, in part because Israel's "Iron Dome" defense system has intercepted many of the projectiles.
Hamas has vowed to keep fighting until Israel and Egypt lift a crippling blockade of Gaza imposed after the Islamic militant group seized power there in 2007.
Hendawi reported from Jerusalem. Associated Press writers Ibrahim Barzak in Gaza City, Yousur Alhlou in Jerusalem and Aron Heller in Kfar Saba, Israel, contributed to this report.