Story highlights At least 61 Palestinians killed, more than 500 injured in Gaza, Palestinian officials say

IDF says it warns civilians when airstrikes are coming with dummy bombs, phone calls

Military is "prepared for all possibilities," Prime Minister Benjamin Netanyahu says

Palestinian Authority President says Israel is committing "genocide"

Israeli airstrikes pounded targets in Gaza, killing scores of people Wednesday as dozens of militant rockets streaked into Israel.

The continued Hamas barrage prompted Israel's Prime Minister to step up the offensive against the militant group.

"The operation will be expanded and will continue until the firing at our communities stops and quiet is restored," Prime Minister Benjamin Netanyahu said.

He did not detail what the expansion would entail but said Israel's military "is prepared for all possibilities."

President Shimon Peres, whose role is largely ceremonial and is not involved in setting policy, said in an exclusive interview with CNN's Becky Anderson that he believed a ground offensive "may happen quite soon" unless Hamas stops firing rockets at Israel.

"We warned them. We asked them to stop it," Peres told Anderson. "We waited one day, two days, three days and they continued, and they spread their fire on more areas in Israel."

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While Peres was speaking on his own and his position may not outline an official government policy, Israeli Intelligence Minister Yuval Steinitz earlier told CNN that a ground operation "might become necessary."

Palestinian Authority President Mahmoud Abbas, meanwhile, convened an emergency meeting of his Cabinet to discuss the crisis.

"This war is not against Hamas or another political party but it is against the Palestinian people," he told the media afterward. "What do you call this crime? What is this crime known under international law? To kill entire families, is this collective punishment?

"This is called collective genocide."

A Hamas spokesman, Sami Abu Zuhri, said Israel's threat to launch a "stupid" ground offensive didn't scare anyone, and fighters from Hamas' military wing were ready to face off with Israel's "coward" soldiers in Gaza.

More deaths in Gaza

The comments came as the death toll rose in Gaza, where the Israel Defense Forces had struck at 550 Hamas targets since launching its offensive Monday.

The IDF said the targets included 60 rocket launchers, 31 tunnels and the homes of 11 senior Hamas leaders, which the IDF described as "command centers."

At least 61 Palestinians have been killed and more than 550 injured in the airstrikes, according to Palestinian medical sources and Health Ministry officials.

Among the dead were eight women and 11 children, including an 18-month-old baby and an 80-year-old woman, according to a list provided by Palestinian medical sources and Health Ministry officials.

In one airstrike Wednesday, two children and their mother were among five people killed when Israeli forces targeted their house. Some members of the family are believed to have links to Hamas, Palestinian security sources said.

A driver for a Gaza news agency was killed Wednesday night when an Israeli missile hit his car, witness told CNN. Three people were wounded, witnesses said.

The IDF said it uses phone calls and drops empty shells on roofs -- what it calls "roof knocking" -- to warn civilians that airstrikes are imminent.

The Israeli Cabinet has authorized the military to call up 40,000 troops if needed. That is 10,000 more than were called up during Israel's offensive into Gaza in November 2012. Only about 1,000 have been mobilized so far.

Teens' deaths sparked new violence

Israel blames Hamas, but the group has denied any involvement.

"Hamas said it clearly. ... We don't have information about what had happened," Osama Hamdan, a foreign policy spokesman for Hamas, told CNN's Michael Holmes.

Only days after the bodies of the Israelis were discovered, a Palestinian teen was abducted, and then found dead , within an hour in Jerusalem. Israel has arrested suspects and says there's "strong indication" it was a revenge killing.

Hamas political leader Khaled Meshaal blamed Netanyahu for the wave of violence.

"It is as if we started the problem in Gaza," he said. "As if a rocket was fired from Gaza so the Zionist enemy was forced to respond to it. This is not true."

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Map of Israel

"I say to the American and European administrations and the United Nations and our Arab neighbors: Were the Palestinian people supposed to break and surrender and die a slow death?" he said. "What is left of our lands and our holy sites? What life is left?"

But with rockets flying over his country's cities, Netanyahu seemed in no mood to back down.

"Our military is strong, the home front is steadfast and our people are united," he said.

The region has many depressing precedents when it comes to violence. Palestinians have revolted twice against Israel's occupation of East Jerusalem, the West Bank and the Gaza Strip. Israel conquered and occupied those territories in the June 1967 war.

In late 2008 and early 2009, Israel carried out airstrikes and then a ground offensive against Hamas in Gaza that killed hundreds of Palestinians. The November 2012 Israeli offensive sparked a bloody eight-day conflict that ended in a cease-fire.

New threat

The IDF said 72 rockets rained down on Israel on Wednesday. Some came down in unpopulated areas, while others were intercepted by the country's Iron Dome defense system over Tel Aviv, Ashkelon and Dimona, the IDF said.

There were no immediate reports of casualties.

Dimona is home to a nuclear plant. Israeli media reported the facility was not hit.

The U.S. Embassy in Tel Aviv said it would close Thursday. Embassy staff had to take shelter Tuesday during a rocket warning, and the facility was already operating with minimal staff.

Hamas is believed to have 10,000 rockets of varying ranges, said Lt. Col. Peter Lerner, a military spokesman. Israel said some 3.5 million residents live in areas within reach of the rockets.