The death toll from Israeli airstrikes on the Gaza Strip rose to 32 in three days after Palestinian officials said on Thursday six members of the same family had been killed.
Triggered by the targeted killing of a top militant in Gaza, the two sides have been exchanging fire since Tuesday, and Israel's military said it has recorded more than 350 incoming rockets.
The Israeli military has been targeting what it said were Islamic Jihad militant sites and rocket-launching squads in the coastal Palestinian enclave of Gaza.
"Six members of the Abu Malhous family, including three children and two women, were killed in an Israeli strike on their family home in Deir al-Balah in the southern Gaza Strip," the Palestinian ministry of health said.
The previous day, Israel said it targeted two Islamic Jihad militants preparing to fire anti-tank missiles.
Air raid sirens wailed and fireballs exploded as air defence missiles intercepted rockets, sending Israelis rushing to bomb shelters.
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In Gaza, residents surveyed damage and mourned the dead outside a mortuary and at funerals.
UN envoy Nickolay Mladenov arrived in Cairo on Wednesday afternoon, airport officials said, following reports he was to hold talks aimed at halting the fighting.
The UN and Egypt have been instrumental in mediating previous ceasefires between Israel and Gaza-based militants.
But a source close to the discussions warned the risk of further escalation remained high.
Israeli Prime Minister Benjamin Netanyahu said Islamic Jihad must stop its rocket attacks or "absorb more and more blows".
Islamic Jihad spokesman Musab al-Barayem said the group was not interested in mediation for now as it retaliated over the killing of one of its commanders.
Israel killed senior Islamic Jihad commander Baha Abu al-Ata and his wife Asma in a targeted strike early Tuesday, prompting barrages of tit-for-tat rocket fire and air strikes.
According to Israel, Ata was responsible for rocket fire at Israel as well as other attacks and was planning more violence, with the military calling him a "ticking bomb."