Gaza, Palestine (BBN)-Israel has ordered thousands of Palestinians in eastern and northern Gaza to leave their homes as it continues air strikes.
The warning came after an Egyptian truce initiative failed to halt militant rocket attacks on Israel, reports BBC.
Hamas initially rejected the truce but an official later told the BBC it would consider a political solution.
Palestinian officials say Israeli raids have killed 194 people so far. Israel on Tuesday reported its first fatality.
The resumption of air strikes come after Israeli Prime Minister Benjamin Netanyahu said he had "no choice" but to step up the military campaign.
"When there is no ceasefire, our answer is fire," Netanyahu said.
The Israel Defense Forces are using recorded telephone messages, warning 100,000 residents of Gaza to leave their homes before 08:00 (05:00 GMT) on Wednesday.
Israel also targeted the house of a senior Hamas official in western Gaza early on Wednesday.
Mahmud al-Zahar, a member of the political bureau of the movement, was not at home at the time.
Israel launched its Operation Protective Edge eight days ago.
Its stated objective is to halt Palestinian rocket attacks on Israel, but the UN says the majority of those killed in Gaza have been civilians.
Hamas says the terms of the ceasefire did not address concerns over the economic blockade of the Gaza strip, which has caused severe economic hardship for many Palestinians.
PM 'A FAILURE'
The Egyptian-backed truce was to have started at 09:00 (06:00 GMT) on Tuesday.
It took six hours for the first attempt to broker a deal between Israel and Hamas to founder.
Israeli PM Benjamin Netanyahu had warned that if the rocket fire continued, Israel would hit back hard – and now it has.
In the search for a ceasefire, this is clearly a setback although not necessarily a terminal blow.
Hamas wants some concessions – like the lifting of the tight restrictions Israel and Egypt impose on Gaza's border – in advance of any deal.
Egypt won't give up on its diplomatic efforts after a single setback but the resumption of hostilities means the question of whether Israel will eventually order ground operations is back on the agenda.
Israel's security cabinet approved it and operations were halted for six hours.
However, Israel then resumed its attacks on Gaza, saying militants had continued to fire dozens of rockets.
Netanyahu said: "This would have been better resolved diplomatically, that's what we tried to do when we accepted the Egyptian truce proposal.
"But Hamas leaves us no choice but to expand and intensify the campaign against it."
One senior Hamas spokesman, Osama Hamdan, told the BBC it had only heard about the truce initiative through the media and that a ceasefire could not be put in place without the details of any agreement being known.
The armed wing of Hamas, the Izz al-Din Qassam Brigades, dismissed the initiative, saying its battle with Israel would "increase in ferocity and intensity".
Under the terms of the Egyptian initiative, the ceasefire should have been followed by a series of meetings in Cairo with high-level delegations from the two sides.
Moussa Abu Marzouk, a top Hamas official, said no final decision had been taken on the Egyptian initiative.
But he told Lebanese TV: "The siege on Gaza must be broken and the people of Gaza should live freely like other people of the world."
Another Hamas leader in Gaza, Mushir al-Masri, told Associated Press that mediators and international guarantees would be needed for any deal to work.
Netanyahu had come under fire in Israel for accepting the truce initiative.
His office announced that deputy defence minister Danny Danon had been sacked for comments branding the PM a "failure".
"It is inconceivable that the deputy defence minister will attack the country's leadership leading the campaign," a statement read.
Israel has mobilised tens of thousands of troops on the border with Gaza amid speculation a ground invasion could be launched.
Israeli defence official Amos Gilad said: "We still have the possibility of going in, under cabinet authority, and putting an end to [the rockets]."
US state department spokeswoman Jen Psaki said Israel had the right to defend itself, but added that "no-one wants a ground war".
The Israel Defense Forces said militants had fired more than 140 rockets into Israel on Tuesday, and more than 1,100 in the past eight days.
A 38-year-old Israeli man was killed by a mortar shell fired from Gaza near the northern border with Israel, reports said.
The UN Relief and Works Agency for Palestine refugees (UNRWA) said on Tuesday that hundreds of thousands of Gazans were without water following the Israeli air strikes and that 560 homes had been destroyed.