Diplomatic efforts to broker a truce in Gaza have intensified, with United Nations Secretary General Ban Ki-moon meeting American Secretary of State John Kerry in Cairo.
Mr Ban is again calling for an immediate and unconditional ceasefire. Nearly 600 Palestinians and 29 Israelis, nearly all soldiers, have died in 14 days of conflict.
The majority of Palestinians killed were civilians, including dozens of children, according to the UN. Israel says it has killed at least 170 militants.
An American state department official said the situation was complicated and it could take several days to bring an end to the fighting.
The United States has pledged $US47 million in humanitarian aid to Gaza, where the latest casualties are reported to be at least five people killed and 70 injured by an Israeli strike on a hospital in Gaza.
The Israeli military said it had targeted a cache of anti-tank missiles in the hospital's "immediate vicinity", the BBC reports.
On Tuesday, Israeli air strikes destroyed several mosques and targeted a stadium and the home of the late leader of Hamas's military wing.
Meanwhile, Israel announced that two more members of the Israel Defense Forces had been killed, taking the number of soldiers killed in fighting to 27. Two civilians have also died.
After the talks with Mr Ban, John Kerry said the United States was concerned about Palestinian casualties, but lent his support to Israel's "appropriate and legitimate" military operation.
Israel launched its ground operation in Gaza after days of air strikes, following rocket fire by militants into Israeli towns.
It says the move is necessary to target Hamas' network of tunnels, which have been used by militants to get into Israel and carry out attacks.