The United Nations Security Council opened urgent talks on efforts to strike a ceasefire deal as Israel ramped up a major military offensive with fresh strikes Monday in the Palestinian territory.
The Palestinian death toll soared to 476 after the bloodiest single day in Gaza in five years, with a spokesman for the enclave's emergency services saying more than a third of Sunday's 120 victims were women and children.
The Israeli army said 13 soldiers had been killed inside Gaza on Sunday, raising to 18 the number of soldiers killed since the ground operation began late on Thursday.
Late Sunday, the armed wing of Hamas claimed it had kidnapped an Israeli soldier, prompting celebrations in the streets of Gaza City and West Bank cities.
"The Israeli soldier Shaul Aaron is in the hands of the Qassam Brigades," a spokesman using the nom-de-guerre Abu Obeida said in a televised address.
Israel's UN ambassador Ron Prosor denied a soldier had been kidnapped, saying: "Those rumors are untrue."
A spokeswoman for the Israeli military said they were investigating the claim.
- Diplomatic push -
During the urgent Security Council talks Palestinian envoy Ryad Mansour called for decisive steps to end the violence, and voiced frustration with what he termed the top world body's failure to take a strong stand.
"The Council failed again and again to shoulder its responsibility," Mansour told reporters.
Prosor noted Israel had agreed to earlier ceasefire offers from Egypt and was acting in self-defense.
Diplomats said no formal statement was expected to emerge from the session.
Speaking with Israeli Prime Minister Benjamin Netanyahu by telephone early Monday, Obama expressed his concern over the deaths on both sides, the White House said in a statement.
In their second call in three days, Obama "reaffirmed Israel's right to defend itself" and called for an "immediate ceasefire" in Gaza.
US Secretary of State John Kerry was flying to Cairo on Monday for meetings with senior officials from Egypt and other countries.
British Prime Minister David Cameron also spoke with Netanyahu, reiterating "the UK's strong support for Israel's right to take proportionate action to defend itself from" Gaza rockets, while expressing condolences over the Israeli deaths and concern over the "mounting civilian casualties in Gaza."
Cameron agreed with Netanyahu that the way out of the "spiral of violence" was through the Egyptian ceasefire initiative, a spokesman for Cameron said.
Ceasefire discussions between Hamas leader Khaled Meshaal and Palestinian president in Qatar were due to take place on Monday after being delayed by a day.
UN chief Ban Ki-moon was also in Doha where he urged Israel to "exercise maximum restraint".
"Too many innocent people are dying...(and) living in constant fear," he told a news conference in Doha.
So far, truce efforts have been rejected by Hamas which has pressed on with its own attacks, undaunted by the Israeli bombardment by land, sea and air.
In the early hours of Monday Israeli jets carried out strikes throughout Gaza, including in southern Rafah and Khan Yunis and northern Beit Lahiya.
Witnesses said warplanes had bombed the home of Hamas politburo member Imad al-Alami in Gaza City, as well as the Khan Yunis home of head of security and police in Gaza, General Saleh Abu Sharekh. No injuries were reported in either attack.
On Sunday thousands of Palestinians fled from Shejaiya, near Gaza City, Shejaiya, after a night of heavy shelling which killed 72, an AFP correspondent reported.
The UN agency for Palestinian refugees UNRWA has opened 61 of its schools to shelter more than 81,000 people who have fled their homes.
The Doctors Without Borders charity urged Israel to "stop bombing civilians trapped in the Gaza Strip", noting the majority of the injured arriving in the Al-Shifa hospital were women and children.
"While the official line is that the ground offensive is aimed at destroying tunnels, what we see on the ground is that bombing is indiscriminate and that those who are dying are civilians," the French NGO said in a statement.
- Netanyahu blames Hamas -
Netanyahu has blamed the civilian casualties on Hamas using innocents "as human shields."
He insisted on Sunday that the military campaign had strong international backing.
"We are carrying out a complex, deep, intensive activity inside the Gaza Strip and there is world support for this... very strong support," he said before a security cabinet meeting.
Although Israel said earlier Sunday it was expanding its ground operation to destroy the network of tunnels used by militants to stage cross-border attacks and fire rockets, Netanyahu said troops could end their mission "fairly quickly".
His Defence Minister Moshe Yaalon also suggested it could end within days, demanding international action to "demilitarise Gaza".
Palestinian militants have over the past 12 days fired 1,414 mortars and rockets that hit Israel, with the Iron Dome air defence system intercepting another 377, the army said.
Thousands participated in rallies in France, Vienna, Stockholm and Amsterdam to oppose Israel's offensive, with a demonstration in the northern Paris suburb of Sarcelles descending into chaos as protesters set fire to bins and looted shops.