CAIRO — With high hopes but low expectations, the U.S. stepped up calls Monday for an international push to end fighting in the Gaza Strip as President Obama sent his top envoy to the Mideast to help broker a new cease-fire between Israel and Hamas militants – the third since 2009. Voicing fresh concern about civilian casualties, Obama reaffirmed his belief that Israel has the right to defend itself against a barrage of more than 1,500 rockets being launched by Hamas.

Yet he said Israel’s military assault of Gaza had already done “significant damage” to Hamas’ network of tunnels, safe havens and other infrastructure, and said he doesn’t want to see more civilians getting killed.

“We have serious concerns about the rising number of Palestinian civilian deaths and the loss of Israeli lives,” Obama said in Washington. “And that is why it now has to be our focus and the focus of the international community to bring about a cease-fire that ends the fighting and can stop the deaths of innocent civilians, both in Gaza and in Israel.”

As Obama spoke, U.S. Secretary of State John Kerry flew to Cairo to join diplomatic efforts to resume a truce that last had been agreed to in November 2012. He will urge the militant Palestinian group to accept a cease-fire agreement offered by Egypt that would halt two weeks of fighting.