"I am calling for an urgent session tonight of the UN Security Council," he said in a televised speech from the Qatari capital Doha. "The situation is intolerable," he said, describing the Israeli attacks as "crimes against humanity".
The number of Palestinians killed in Israeli attacks in the Gaza Strip on Sunday was at least 100, the emergency services spokesman in the territory, Ashraf al-Qudra, said.
The vast majority of Sunday's dead were in Shejaiya between Gaza City and the Israeli border, with at least 62 people killed there in a blistering bombardment which began overnight, emergency services spokesman Ashraf al-Qudra said.
At least 250 were wounded, raising the overall injury toll during the 13 days of violence to well above 3,000, he said.
Relatives of Palestinians killed during the overnight shelling of the eastern Gaza district of Shejaiya by the Israeli army arrive at the morgue of the al-Shifa hospital in Gaza City. (AFP photo)
Of the 437 people killed since the operation began, more than a third were women and children, Qudra said.
Also on Sunday, the Israeli army said 13 soldiers were killed in fighting inside the enclave.
"Over the course of the day, 13 soldiers from the IDF's Golani Brigade were killed in combat in the Gaza Strip," an army statement said.
Their deaths raised to 18 the total number of soldiers killed since Israel began a ground operation in Gaza late on Thursday, in what was the highest casualty figure since the 2006 Lebanon war.
Dozens more have been wounded.
Most of Sunday's Palestinian victims were killed in a blistering hours-long Israeli assault on Shejaiya near Gaza City, which began before dawn and has so far claimed 62 Palestinian lives.
With ambulances unable to reach the area, the International Committee of the Red Cross called for an urgent temporary ceasefire to allow paramedics to evacuate the dead and wounded, which was agreed on by the two sides.
Inside the ravaged neighbourhood, there were hellish scenes of carnage and chaos as a convoy of ambulances moved in to make the most of the calm, an AFP correspondent said.
Entire buildings were collapsed on themselves or strewn into the streets, while others were still ablaze, sending pillars of black smoke skywards.
There were also bodies, blackened and charred almost beyond recognition, some with whole limbs missing.
As the violence raged, Palestinian president Mahmud Abbas arrived in Qatar to discuss a ceasefire with Hamas leader Khaled Meshaal, with UN chief Ban Ki-moon due there later Sunday at the start of a regional tour to push truce efforts.
So far, truce efforts have been rejected by Hamas.
Undaunted by the Israeli bombardment by land, sea and air, it has pressed on with its own assaults.
Israelis soldiers flash the victory sign on their armoured personnel carrier (APC) at an army deployment near Israel's border with the Gaza Strip. (AFP photo)
Following a night of terror in Shejaiya, thousands began fleeing for their lives at first light after heavy shelling left casualties lying in the streets, an AFP correspondent reported.
Clouds of black smoke billowed into the sky as the shelling continued and Gaza's eastern flank burned.
Among those fleeing was a group of gunmen with automatic weapons, some with their faces covered by scarves.
Women and children were among the dead, as were a Palestinian paramedic and a cameraman killed when the ambulance they were in was hit.
"He wasn't a fighter, he was a fighter for humanity," wailed one relative as the family buried him.
"He was an ambulance worker, did he deserve to die?"
So far, UNRWA has opened 61 of its schools to shelter those fleeing the most heavily bombarded areas, with more than 81,000 people taking refuge in them, the agency said.
Israeli Prime Minister Benjamin Netanyahu has put the blame for civilian casualties squarely on Hamas, accusing it of "using innocent civilians as human shields".
A medic helps a Palestinian in the Shejaia neighbourhood, which was heavily shelled by Israel during fighting, in Gaza City. (Reuters photo)
An end in sight?
Speaking 24 hours after the ground operation began, Israel's Chief-of-Staff Lieutenant General Benny Gantz warned there would be "moments of hardship", alluding to the possibility of further Israeli casualties.
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, Netanyahu also said troops could end their mission "fairly quickly".
But he demanded international action to demilitarise the tiny coastal enclave, which is home to 1.7 million Palestinians and is one of the most densely populated areas on the planet.
"I think the international community has to... undertake a programme to demilitarise Gaza and to change the situation because it's unacceptable," he told CNN's "State of the Union" talk show.
US secretary of state John Kerry blamed Hamas for perpetuating the conflict, urging it to "be responsible and accept... a multilateral ceasefire without conditions".
But Turkey's Prime Minister Recep Tayyip Erdogan accused Israel of killing Palestinians "mercilessly" and lashed out at Washington for turning a blind eye to Gaza's suffering.
Palestinian relatives grieve as mourners carry the bodies of two brothers who where killed at their family house in an airstrike, during their funerals in Rafah in the southern Gaza Strip. (AP photo)
"How can we ignore this? How can a country like the United States turn a blind eye to this?" he asked.
"As a member of the UN Security Council, it needs to act fairly."
Meanwhile, at Gaza City's Shifa hospital, casualties were being brought in by the minute during the morning, among them many children peppered with shrapnel wounds and screaming in agony.
"This is the worst I've ever seen it," said Dr Said Hassan, who has worked at the hospital for eight years.
Obama sending Kerry to Cairo for talks
US President Barack Obama expressed concern over the loss of life in Gaza in a call to Israeli Prime Minister Benjamin Netanyahu Sunday, and said secretary of state John Kerry will travel to Cairo to seek an end to the fighting.
Obama, who condemned attacks by Hamas on Israel, "also raised serious concern about the growing number of casualties, including increasing Palestinian civilian deaths in Gaza and the loss of Israeli soldiers," the White House said, adding that Kerry will travel "soon" to the Egyptian capital.
The UN Relief and Works Agency said that 81,000 displaced people had now taken refuge in 61 UNRWA shelters in Gaza. Egypt, Qatar, France and the United Nations, among others, have all been pushing, with little sign of progress, for a permanent ceasefire in the worst surge of Israeli-Palestinian fighting in two years.
US Secretary of State John Kerry said he might travel to the Middle East soon to try to aid truce efforts. He said he supported Israel's efforts to destroy tunnels it says Gaza militants use for infiltration attempts and to hide weaponry.
"We support Israel's right to defend itself against rockets that are continuing to come in," Kerry told Fox News. Washington has also urged Israel to minimise civilian casualties.
Qatar was due to host a meeting between Abbas and UN secretary-general Ban Ki-moon on Sunday, a senior Qatari source told Reuters. Ban was due to travel to Kuwait, Egypt, Israel, the Palestinian Territories and Jordan during the week, a UN statement said.
The Qatari source said Abbas would also meet Hamas leader Khaled Meshaal.
Western-backed Abbas in April struck a reconciliation deal with Hamas, which seized the Gaza Strip in 2007 from forces loyal to his Fatah movement. The agreement led to the formation of a Palestinian unity government and Israel's pullout from US-brokered peace talks.
Hamas has already rejected one Egyptian-brokered truce, saying any deal must include an end to a blockade of the coastal area and a recommitment to a ceasefire reached after an eight-day war in Gaza in 2012.
Hostilities escalated following the killing last month of three Jewish students that Israel blames on Hamas. Hamas neither confirmed nor denied involvement.
The apparent revenge murder of a Palestinian youth in Jerusalem, for which Israel has charged three Israelis, further fuelled tension.
(With inputs from Reuters and AFP)