The escalating violence has raised concerns of the international community which has largely remained mute in the past few days.
Despite the international pressure, Israeli Prime Minister Benjamin Netanyahu said his country would continue the campaign and did not rule out a ground offensive, Xinhua reported.
"I will end it when our goals are realised. And the overriding goal is to restore peace and quiet," Netanyahu said in a nationally televised news conference Friday.
Israel began the assault Tuesday in what it said was a response to weeks of heavy rocket fire out of the Hamas-controlled Gaza. In four days, more than 1,000 targets in Gaza have been pummeled by Israel's airstrikes.
Among the Palestine casualties, two-thirds are civilians, including children, women and old men, according to the Palestinian health ministry, which added that the total number of wounded went up to around 700 people as the Israeli air offensive entered the fourth day.
Netanyahu rejected criticism of the death toll among civilians, saying that Israel does everything possible to protect them. He accused Hamas of putting civilians in harm's way by using residential areas for cover.
Officials from the Islamist Hamas movement said the group would only accept a ceasefire if it got something in return, such as restoration of the 2012 truce and the release of prisoners arrested by Israel in a recent crackdown.
While the crisis shows no signs of abating, diplomatic efforts from outside have gathered pace to end the hostilities.
UN High Commissioner for Human Rights Navi Pillay Friday expressed her concern over the civilian casualties in the attack, saying that the reports raise "serious doubt about whether the Israeli strikes have been in accordance with international humanitarian and human rights laws".
UN Secretary General Ban Ki-moon Thursday also warned of the "risk of an all-out escalation in Israel and Gaza", urging Israelis and Palestinians to find common ground for a return to calm and a cease-fire understanding.
The US, while affirming Israel's right to defend itself, offered help in truce negotiations.
"There are a number of relationships the United States has that we are willing to leverage in the region to try to bring about an end to the rocket fire that's originating in Gaza," Josh Earnest, White House spokesman, said Friday.