UN chief Ban Ki-moon and US Secretary of State John Kerry are in Cairo trying to broker a truce between Israel and Hamas after two weeks of fighting which has left more than 570 Palestinians dead.
Many of those killed in the relentless Israeli campaign of shelling and airstrikes in the Gaza Strip, which entered its 15th day, were women and children. On the Israeli side 27 soldiers and two civilians have died.
World powers have urged Hamas to accept an Egyptian-brokered ceasefire and stop raining rockets into Israel from the Gaza Strip, demands it has so far resisted.
"Only Hamas now needs to make the decision to spare innocent civilians from this violence," Kerry said, and UN chief Ban Ki-moon appealed for the violence to "stop now".
Kerry, who arrived in Cairo to try and intensify truce efforts, pledged $US47 million ($NZ54.15 million) in humanitarian aid for the battered Gaza Strip.
Arab League chief Nabil al-Arabi too urged Hamas to accept an Egyptian proposal to end the fighting it had turned down last week.
Kerry plans to hold his meetings on Tuesday with the Egyptian leadership including President Abdel Fattah al-Sisi.
However, US officials acknowledge that the truce efforts could prove trickier than in the past as Egypt - long the key regional broker - had little leverage with Hamas after the army overthrew Islamist president Mohamed Morsi last year.
The top US diplomat defended ally Israel's right to strike against Hamas militants, but voiced concern over the massive civilian violence.
"We are deeply concerned about the consequences of Israel's appropriate and legitimate effort to defend itself," he told reporters as he met with the UN chief, urging Hamas to accept the Egyptian-proposed ceasefire.
Smoke from Israeli strikes rises over Gaza City, in the Gaza Strip. Photo / AP
Ban said Hamas "should immediately stop firing rockets", adding that while he understood Israel's military response, "there is a proportionality and ... most of the death toll (has been) Palestinian people".
Fresh Israeli strikes continued on Tuesday and Gaza emergency services spokesman Ashraf al-Qudra reported the Palestinian death toll since Israel launched its operation on July 8 was now 576.
Israel says its campaign aims to stamp out rocket fire from Gaza, and the ground phase of the operation to destroy tunnels burrowed into Israel by Hamas, the main power in the coastal strip.
Since the offensive began huge numbers of Gazans have fled their homes, with the UN saying more than 100,000 people have sought shelter in 69 schools run by its Palestinian refugee agency (UNRWA).
Meanwhile, Hamas leader Khaled Meshaal and Palestinian president Mahmud Abbas held talks in Doha, pledging to work together for a ceasefire and to lift the blockade on Gaza.
But there has been no let-up since the operation began with 116 rockets hitting Israel on Monday, one striking the greater Tel Aviv area, and another 17 shot down, the army said.
Violence also broke out in the West Bank, where an Israeli shot dead a Palestinian who had been throwing stones at his car, Palestinian security sources said.