The Palestinian death toll in an Israeli offensive in the Gaza Strip jumped to more than 500 on Monday, as the United States, alarmed by escalating civilian bloodshed, took a direct role in efforts to secure a ceasefire, Reuters reported.
Despite growing calls for a halt to two weeks of fighting, violence raged on, with Israel saying it had killed 10 militants who tunnelled across the border from Gaza, and Palestinian officials accusing the Israeli army of shelling a hospital.
Israeli jets, tanks and artillery constantly pounded the densely-populated coastal strip, killing 28 members of a single family at the southern end. Hamas unleashed regular volleys of rockets at Israeli cities, many of them intercepted.
A day after he was caught by an open microphone saying sarcastically that the Israeli assault was "a hell of a pinpoint operation", U.S. Secretary of State John Kerry flew to Cairo to try to secure an end to hostilities.
Speaking in Washington, President Barack Obama said he was increasingly worried by the conflict.
"We have serious concerns about the rising number of Palestinian civilian deaths and the loss of Israeli lives, and that is why it now has to be our focus and the focus of the international community to bring about a ceasefire," he told reporters at the White House.
The Islamist group Hamas, which inflicted the biggest single loss on Israeli forces in eight years when it killed 13 soldiers in Gaza on Sunday, said it would not lay down its arms until a series of demands were met - including an end to a blockade imposed on the territory by both Israel and Egypt.
"The world must understand that Gaza has decided to end the blockade by its blood and its heroism," deputy Hamas leader Ismail Haniyeh said in a televised address.
At Al-Aqsa hospital in the central Gaza Strip, four people were killed and 70 wounded when an Israeli tank shell slammed into the third floor, housing operating theatres and an intensive care unit, the Health Ministry said.
The Israeli military, which has accused Hamas militants of firing rockets from the grounds of Gaza hospitals and seeking refuge there, had no immediate comment.
Non-stop attacks lifted the Palestinian death toll to 518, including almost 100 children, since fighting started on July 8, Gaza health officials said. Israel says 18 of its soldiers have also died along with two civilians.