US Secretary of State John Kerry is to push for an "immediate" ceasefire in Gaza when he arrives later Monday in Cairo, President Barack Obama said.
Obama also said that while Israel has the right to defend itself against a barrage of Hamas rockets, Washington has "serious concerns about the rising number of Palestinian civilian deaths and the loss of Israeli lives."
"That is why it now has to be our focus and the focus of the international community to bring about a ceasefire that ends the fighting and that can stop the deaths of innocent civilians, both in Gaza and in Israel," he said.
Kerry was headed to Egypt, which has been a mediator in past Israel-Palestinian conflicts and has taken the lead in trying to broker a truce between Israel and its Islamist foe Hamas, which dominates the Gaza Strip.
The two-week conflict has dramatically escalated in recent days, with Israeli ground forces pushing into Gaza, where the Palestinian death toll stood at 548 as of late Monday.
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Obama noted that Israel had "already done significant damage to Hamas's terrorist infrastructure in Gaza."
Eighteen Israeli soldiers have also died, the army's worst death toll in years.
"The work will not be easy," Obama said of efforts to broker a ceasefire.
"Obviously, there are enormous passions involved in this, and some very difficult strategic issues involved," the president added, in a statement delivered from the White House.
"Nevertheless, I've asked John to do everything he can to help facilitate a cessation to hostilities. We don't want to see any more civilians getting killed."