Story highlights President Obama speaks with Prime Minister Benjamin Netanyahu by phone

Palestinian groups say there were 70 strikes on Wednesday

An Israeli spokesman calls the operation defensive after rocket attacks from Gaza

Ahmed al-Ja'abari, the head of Hamas' military wing, was killed in the first strike

Israel launched a series of blistering airstrikes Wednesday on what it says are terrorist targets in Gaza, killing the chief of Hamas' military wing and at least eight others, Israeli and Palestinian officials said.

As the tensions ratcheted up, the U.N. Security Council held an emergency meeting Wednesday evening.

Palestinian leaders immediately condemned the attacks as an escalation, with President Mahmoud Abbas calling for an emergency session of the Council of the League of Arab States to discuss what he called Israeli "aggression," the Egyptian state news agency MENA reported.

Hamas' military wing warned that Israelis had opened "the gates of hell on themselves" with the move.

A report on the Israel Defense Forces website said Brig. Gen. Yoav Moredechai would not rule out a ground attack.

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Map: Israel

"Infantry brigades have been shifted in preparation for the operation," he said, according to the website.

Israeli military spokeswoman Lt. Colonel Avital Leibovich said: "There are some reserve units that are preparing but nothing more than that at this point."

There were at least 70 strikes by warplanes and ships Wednesday, officials from Palestinian militant groups said. As night fell, more airstrikes could be heard, and Hamas security officials said four more attacks hit empty swaths of farmland in Gaza late Wednesday. The IDF said at least 128 rockets had been fired from Gaza since Saturday.

Israel's Iron Dome air defense system intercepted 28 rockets launched at Israel on Wednesday, the IDF said on its Twitter feed , which it was updating almost hourly with new details as well as links to photos.

One of the posters on the IDF's feed was Al-Qassam, the military wing of Hamas, which has the Twitter ID of Alqassam Brigades

It wrote: "@idfspokesperson Our blessed hands will reach your leaders and soldiers wherever they are (You Opened Hell Gates on Yourselves)."

Palestinian medical sources said at least eight people died in the Israeli airstrikes, including two young girls, and 84 others were wounded, 10 in serious condition. However, the health minister in Gaza, Mufid al-Mukhalalati, put the death toll at seven.

The dead included Ahmed al-Ja'abari, the popular and influential head of the Hamas military wing, and his son, the group said on its website.

The Israeli operation -- which the military calls "Operation Pillar of Defense" -- came after Prime Minister Benjamin Netanyahu warned this week of pending retaliation by Israel for increased rocket attacks from Gaza.

"I would ask you, I'd ask any person around the planet: What would you do if your population was targeted day after day?" Israeli government spokesman Mark Regev said, later adding that "you have to see our operation as fundamentally defensive."

Egypt recalled its ambassador to Israel on Wednesday, the Israeli Foreign Ministry said. A senior Israeli official said its ambassador to Egypt returned home, but that move wasn't related to the ongoing violence. The official wouldn't comment on whether Israel had pulled its entire diplomatic staff from Egypt.

The United States said Israel has the right to defend itself, according to a statement from the State Department.

"We strongly condemn the barrage of rocket fire from Gaza into southern Israel, and we regret the death and injury of innocent Israeli and Palestinian civilians caused by the ensuing violence," the statement said. "There is no justification for the violence that Hamas and other terrorist organizations are employing against the people of Israel. We call on those responsible to stop these cowardly acts immediately."

The White House said in a news release that President Obama spoke with Netanyahu by phone, reiterating the United States support for Israel. Obama also spoke with Egyptian President Mohamed Morsy and the two agreed it was important to help de-escalate the situation quickly, the White House statement said.

A spokesman for Hamas, Osama Hamdan, claimed that Hamas has been defending itself from Israeli attacks.

"I think the ones who declared war was Israel, and I think the Palestinians are in the position of defending themselves and nothing more than this," he said. Hamas will resist as long as the Israeli offensive lasts, Hamdan said.

Israeli navy ships could be seen firing into Gaza from the Mediterranean. The navy struck "terror sites" there, the IDF said via Twitter.

The Israeli military said in a statement Wednesday it targeted "a significant number of long-range rockets sites" to deliver "a significant blow" to Hamas' underground rocket-launching capabilities and munitions warehouses.

Some of the munitions warehouses were in civilian residential buildings, which showed that Hamas uses a strategy of human shields, Israeli military sources said.

"The aim of targeting these sites is to hamper their rocket-launching weapons build up capabilities," the IDF statement said, adding that the Gaza strip had become "a frontal base for Iran firing rockets and carrying out terrorist attacks against Israeli citizens."

Angry crowds gathered at the heavily damaged vehicle that contained the bodies of al-Ja'abari and his bodyguard.

Saeb Erakat, the chief Palestinian negotiator, condemned "in the strongest possible terms" what he called the Israeli assassination of al-Ja'abari.

In an interview with CNN, Erakat labeled the attack the beginning of a "major, major Israeli escalation," and he called on the international community to pressure Israel to halt its operation.

Al-Mukhalalati, the Gaza health minister, also called on "the free world to stop this massacre committed by Israel."

Asked about assassinating al-Ja'abari, Regev said the Hamas military leader headed a "terror military machine."

"This is the man with blood on his hands. This man is a known and wanted terrorist," he said. "In taking him out, Israel was acting legitimately."

The latest escalation in violence is part of a cycle of attacks between periods of relative stability between Israel and the Palestinians.

"This was both inevitable and predictable," said Aaron David Miller, a Middle East expert and vice president at the Woodrow Wilson Center.

There is no long-term basis for both sides to find a lasting peace, he said.

Israel and the Palestinians have "completely different political and strategic goals," Miller explained. The focus should be on how to bring security until a basis for long-term stability arises, he added.