Israeli warplanes have struck Gaza, killing the wife and child of Hamas' top military chief, the Islamist movement says, after truce talks in Cairo collapsed in a storm of violence.
It was not immediately clear whether Mohammed Deif himself, who has topped Israel's most wanted list for decades, was killed or wounded in the strike which hit a house in Gaza City late on Tuesday.
Hamas vowed bloody revenge, saying Israel had "opened the gates of hell".
The deadly attack came just hours after a resumption of the fighting in and around Gaza after more than a week of calm, as Egyptian negotiators pushed the warring sides to broker a decisive end to six weeks of bloodshed.
The strike killed two and injured another 45, medics said, with Hamas confirming early on Wednesday that those who died were the wife and child of Deif, who heads its armed wing, the Ezzedine al-Qassam Brigades.
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Emergency services spokesman Ashraf al-Qudra initially said three people were killed in the strike, among them an unidentified man, but later revised the toll down to two. He did not explain why.
He named the victims as Widad Deif and her seven-month-old son, Ali.
Millions in Gaza and southern Israel spent another sleepless night as terror returned to the skies, with air strikes and rocket fire ending an extended lull brought on by back-to-back truce agreements.
Since the violence resumed on Tuesday afternoon, shattering more than a week of calm, at least 12 people have been killed in scores of Israeli strikes across Gaza, Qudra said.
A second deadly strike early on Wednesday killed seven people in the central town of Deir al-Balah, among them a heavily-pregnant woman and three children, he added.
In the same period, Gaza militants fired at least 80 rockets over the border, of which between 40 and 45 had hit southern and central Israel while another 24 were shot down, an army spokeswoman said.
The army had hit 78 targets across Gaza, she added.
So far, the bloodshed in Gaza which erupted on July 8 has claimed the lives of 2029 Palestinians and 67 on the Israeli side. The UN says around three quarters of the victims in Gaza were civilians.
Tuesday's violence left Egyptian truce efforts in tatters, with Israeli Prime Minister Benjamin Netanyahu immediately ordering the delegation back from Cairo. Israel has repeatedly said it would never negotiate under fire.
Most of the Palestinian negotiators, including delegation head Azzam al-Ahmed, also left Cairo.
"We are leaving ... but we have not pulled out of negotiations," he said, saying the Palestinians had handed a truce proposal to Israel and were waiting for the answer.
"We will not come back (to Cairo) until Israel responds."
Egypt expressed "profound regret at the breach of the ceasefire in Gaza" and said it was working to bring both sides back to the negotiating table, a foreign ministry statement said.
