Israel has resumed its air strikes on Hamas-controlled Gaza, after Israel's brief truce was met with continuing rocket fire.
Israel had earlier accepted an Egyptian ceasefire proposal and halted operations on Tuesday morning.
But the armed wing of Hamas rejected the initiative as a "surrender", according to the BBC.
Palestinian officials said 192 people have been killed in eight days of Israeli air strikes. Israel on Tuesday reported its first fatality.
Israel says it launched Operation Protective Edge to stop militants firing rockets into Israel.
Prime Minister Benjamin Netanyahu said on Tuesday evening that Israel had "no choice" but to step up its operations.
He said: "Hamas chose to continue fighting and will pay the price for that decision. When there is no ceasefire, our answer is fire."
The Israel Defense Forces said militants had fired 125 rockets into Israel on Tuesday.
A 38-year-old Israeli man was killed by a mortar shell fired from Gaza near the northern border with Israel, reports said.
The IDF said that after resuming its air strikes, 30 targets had been attacked in Gaza, including 20 concealed rocket launchers, tunnels, a weapon storage facility and operational infrastructure used by a senior militant.
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.
There has been no definitive response to the initiative from Hamas.
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".
US Secretary of State John Kerry said he could not "condemn strongly enough" Hamas' actions in continuing to fire rockets.
Israeli government spokesman Mark Regev told the BBC: "Hamas had seven hours to get their act together and they have rejected this ceasefire proposal... it's rejected it both in word and in deed."