Diplomatic efforts to broker a truce in Gaza have intensified, with US Secretary of State John Kerry meeting the UN chief Ban Ki-moon in Cairo.
Mr Kerry said the US was concerned about Palestinian casualties, but lent his support to Israel's "appropriate and legitimate" military operation.
He said the US was sending $47m (£28m) in aid to Gaza "to try to alleviate the immediate humanitarian crisis."
The two-week conflict has left nearly 600 Palestinians and 29 Israelis dead.
Early on Tuesday, Israel announced that two more members of the Israel Defense Forces (IDF) had been killed, taking the number of soldiers killed in fighting to 27. Two civilians have also died.
Monday's attacks across Gaza killed at least 56 people including 16 children, Gazan health officials said, with the Palestinian death toll now at more than 560.
The IDF says it has killed more than 170 militants since Thursday night, when it launched its ground offensive.
Mr Kerry arrived in Egypt on Monday to step up efforts to find a diplomatic solution to the current crisis between Israel and Hamas. He is expected to stay in Cairo until at least Wednesday.
He urged Hamas to "make the decision to spare innocent civilians," a call echoed by Arab League chief Nabil al-Arabi, who said the group should accept an Egyptian proposal to end the fighting.
Hamas rejected that proposal last week, with its armed wing saying agreeing to it would be a "surrender".
The UN Security Council has issued a call for an "immediate cessation of hostilities", but did not endorse a strongly worded draft resolution backed by Arab states.
Mr Ban reiterated the call for an immediate and unconditional ceasefire ahead of travelling to Israel and the Palestinian Territories later on Tuesday.
He said he appreciated Israel's right to defend itself against Hamas, but said restrictions on Gaza should be lifted "so that people should not resort to this kind of violence as a way of expressing their grievances".
On Monday, an Israeli airstrike on a hospital in Gaza killed at least five people and injured 70.
The Israeli military said it had targeted a cache of anti-tank missiles in the hospital's "immediate vicinity".
Palestinian television showed footage of wounded people being treated after the strike at the Al-Aqsa Hospital in Deir al-Balah in the central Gaza Strip.
Doctors say several Israeli tank shells hit the hospital's reception, intensive care unit and operating theatres.
Most of the wounded were doctors, according to Palestinian officials.
In a statement, the IDF said: "Civilian casualties are a tragic inevitability of [Hamas'] brutal and systematic exploitation of homes, hospitals and mosques in Gaza."
The UN relief agency says more than 100,000 people have sought shelter in its facilities because of the conflict, double the number of people that did so in the Gaza conflict in 2009.
Israel sent ground troops into Gaza after days of heavy air and naval barrages failed to stop rocket fire.
Israel says the ground operation is necessary to target Hamas' network of tunnels, which have been used by militants to get into Israel and carry out attacks.
But the UN, Palestinians and Arab states have expressed alarm at the growing number of civilian casualties.
(BBC)
