Israeli warplanes have kept up deadly raids on Gaza but failed to stop Palestinian militants firing rockets across the border, as the United States offered to help negotiate a truce yesterday.
With the violence growing worse, US President Barack Obama in a phone call to Israeli Prime Minister Benjamin Netanyahu said his Government was willing to broker a ceasefire.
Obama said he was concerned the fighting could escalate and "called for all sides to do everything they can to protect the lives of civilians", the White House said.
"The United States remains prepared to facilitate a cessation of hostilities, including a return to the November 2012 ceasefire agreement."
The 2012 deal, brokered by former Secretary of State Hillary Clinton and Egypt, ended eight days of Israeli airstrikes on Hamas targets in a previous showdown.
Appeals for an immediate truce also came from United Nations chief Ban Ki Moon at an emergency meeting yesterday of the Security Council, saying a ceasefire was "more urgent than ever".
Russian President Vladimir Putin issued a similar plea in a phone call to Netanyahu, urging an immediate end to the bloodshed and expressing concern over civilian casualties.
But Israel appeared bent on dealing a fatal blow to the Islamist movement Hamas, which controls Gaza, with Netanyahu reportedly saying talk of a ceasefire was "not even on the agenda".
Israeli air strikes killed more than 30 Palestinians yesterday alone, many of them women and children.
Hamas, the Palestinian group ruling Gaza, also appeared to have no interest in letting up, striking deep inside Israel over the past 48 hours, with rockets crashing down near Jerusalem and Tel Aviv and even as far away as Hadera, 116km to the north.
Senior Hamas member and the movement's former Gaza Prime Minister Ismail Haniya ruled out any backing down by the Islamist movement.
"The enemy [Israel] is the one that started this aggression and it must stop, because we are [simply] defending ourselves," Haniya said yesterday.
Sirens wailed across Jerusalem for the second time running yesterday and a series of loud explosions echoed across the city as the Iron Dome anti-missile system shot down two rockets fired from Gaza, the army said.
Another two crashed down in open areas in the occupied West Bank, witnesses and security officials told AFP.
Hamas claimed to have fired four missiles at Jerusalem.
Later six Palestinians were killed in two attacks on Gaza, five of them - including a woman and a 7-year-old child - in a strike on the home of an Islamic Jihad militant in Rafah, said Gaza's emergency services spokesman Ashraf al-Qudra.
Since the start of the Israeli campaign on Tuesday, around 95 Palestinians have been killed and more than 500 injured, according to al-Qudra.
"We are still facing a difficult, complex and complicated campaign," Netanyahu said after a security Cabinet meeting.
Israel has confirmed preparations are being made for a possible ground attack, with tanks seen massing along the border and Netanyahu facing mounting pressure from coalition hardliners to put boots back on the ground in the territory from which Israeli troops and settlers withdrew in 2005.
Since the start of the operation, the Israeli military's biggest offensive on Gaza since November 2012, its forces have hit over 1090 "terror sites".
In the same period, Gaza militants fired 407 mortars and rockets that struck Israel, while a further 118 rockets were intercepted, an army spokeswoman said yesterday.