Palestinians on Wednesday accused Israel of attempting to assassinate the top Hamas military commander in the Gaza Strip as the hopes for a cease-fire were dashed by a day-long exchange of taunts and threats, alongside escalating rocket fire and airstrikes that left 22 Palestinians dead.

In a brief news conference outside the headquarters of the Israel Defense Forces, Prime Minister Benjamin Netanyahu said Wednesday that all combatants in the Palestinian militant factions were legitimate targets.

“No Hamas member is immune," Netanyahu said.

He warned Hamas, which controls the Gaza Strip, that continued rocket fire directed at Israel “will be hit back sevenfold.”

Hamas, though, was not backing down. In a televised statement Wednesday, a masked representative for the Hamas military wing, known as the Qassam Brigades, warned that Hamas rockets would begin to strike Israel’s strategic interests, including Ben Gurion Airport outside Tel Aviv, on Thursday morning.

The Hamas militant mocked Israel for what he described as a failed attempt on Tuesday to assassinate Mohammed Deif, the top commander of the Qassam Brigades.

Israeli F-16s fired six missiles at the Gaza City home of Mohammed Yassin Dalu, reportedly the head of the Hamas rocket division. The Palestinians said that Israel believed Deif was inside the home. Instead, they said, Deif's wife and infant son were killed in the attack.

“You have failed, and you have missed,” the Hamas spokesman said.

The bellicose rhetoric and exchange of fire came a day after negotiations for a permanent truce broke down.

Palestinian militants in Gaza fired more than 150 rockets at Israel in the 24 hours after the cease-fire fell apart Tuesday. Israel hit dozens of sites in Gaza. The Gaza Health Ministry said 22 people were killed by Israel.

Hamas claimed it launched two rockets at an Israeli natural gas platform in the Mediterranean Sea, the first attempt of its kind.

“We remain very concerned about developments in Gaza,” State Department spokeswoman Marie Harf said Wednesday. “We call for an immediate end to rocket fire and hostilities and a return to cease-fire talks.”

Secretary of State John F. Kerry discussed Gaza and efforts toward a cease-fire with Netanyahu on Wednesday, Harf said, without providing further details. She repeated that the United States supports Israel’s right to defend itself.

Israel said militants in Gaza broke a temporary cease-fire on Tuesday afternoon by launching three rockets into Israel. The Hamas leadership denied that its fighters fired the salvo and accused Israel of seeking to create an excuse for breaking off truce talks in Cairo.

“This was a pretext to target a senior member of Hamas and to withdraw the delegation, and to end the cease-fire,” Mousa Abu Marzook, a founder and senior leader of Hamas, said on his Facebook page.

Abu Marzook, who was a part of the Palestinian delegation in Cairo, said the Israeli attack against the family of “the great leader” Deif was “a war crime.”

The shadowy leader of the Qassam Brigades is reported to be the mastermind behind extensive tunnel networks in Gaza. Israeli officials say Deif has waged terrorist campaigns and an asymmetric war against Israel for decades, and he has survived repeated Israeli attempts to assassinate him, earning him the moniker “the cat with nine lives.”

“I think that the worst is still to come,” chief Palestinian negotiator Saeb Erekat told Voice of Palestine radio.

Earlier, a leader in Netanyahu’s coalition government, Economy Minister Naftali Bennett, said Israel was wasting its time negotiating with terrorists.

Amos Yadlin, the former chief of Israeli military intelligence and now director of Tel Aviv University’s Institute for National Security Studies, said the gloves are now off. “When you fight your enemy you go to the head of the snake, not the tail of the snake,” he said.

Israel claims it has killed 900 “terrorists” in more than a month of fighting in Gaza. But Israel has not killed any senior Hamas leaders.

Yadlin said the likely reason was intelligence gaps or concerns that collateral damage would be too high.

“Instead of fighting like ordinary terrorists, they hide deep underground or behind many, many civilians,” he said. “They were too cowardly to come and fight.”

The assassination attempt against Deif puzzled some Israeli and foreign analysts. Why would Deif take the risk of going to the home of a senior Hamas militant on the day the cease-fire was falling apart?

“It seems unlikely that, after more than five hours of Israeli airstrikes on Wednesday, the only senior Hamas figure not underground in a bunker was Israel’s number one target, Mohammed Deif, who decided it was a good time to visit his wife and infant son,” said Nathan Thrall, a senior Middle East analyst with the International Crisis Group.

Giora Eiland, former head of Israel’s national security council, said that “there are three options”: Deif was killed and Hamas is denying it, or he was there but not killed, or he was not there at all. “If it is the latter, then this is something that the Israeli intelligence cannot be very proud of.”

Eiland said Deif represents a symbolic target. “Deif is a kind of Osama bin Laden for the Israelis,” he said. “If he is killed, it gives both the public and the politicians some sort of satisfaction.”