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JERUSALEM -- With rockets raining deep inside Israel, the military pummeled Palestinian targets Wednesday across the Gaza Strip and threatened a broad ground offensive, while the first diplomatic efforts to end two days of heavy fighting got underway.
Egypt, which has mediated before between Israel and the Hamas militant group, said it spoke to all sides about ending the violence. U.S. Secretary of State John Kerry was in touch with Israel to try to lower tensions. And the United Nations chief warned of a "deteriorating situation ... which could quickly get beyond anyone's control."
As the Palestinian death toll rose above 60, neither side showed any sign of halting their heaviest fighting since an eight-day battle in late 2012.
Israel said it hit more than 300 targets and Hamas positions throughout Gaza, including rocket-launchers, weapons-storage sites and tunnels that it said the group uses to carry out attacks. The military said 74 rockets landed in Israel, including one that reached the northern city of Hadera, the deepest rocket strike ever from Gaza.
"Hamas will pay a heavy price for firing toward Israeli citizens," Prime Minister Benjamin Netanyahu said. "The operation will expand and continue until the fire toward our towns stops and quiet returns."
Israel began the offensive Tuesday in response to weeks of rocket launches, and officials said the airstrikes would continue until the firing stops. At least 20 civilians were among the 61 deaths reported by the Health Ministry in Gaza. There have been no serious casualties on the Israeli side.
Thousands of Israeli troops massed near the Gaza border, the possibility of a ground invasion grew larger -- along with the risk of heavier casualties on both sides.
"Despite the fact it will be hard, complicated and costly, we will have to take over Gaza temporarily, for a few weeks, to cut off the strengthening of this terror army," Yuval Steinitz, Israel's intelligence minister, told Israel Radio.
"If you ask my humble opinion, a significant operation like this is approaching."
The government has authorized the army to activate up to 40,000 reservists, and Israeli TV stations said about a quarter of those forces had been called up, signaling a decision on a ground invasion could still be days away.
A ground offensive in Gaza would be a risky gamble for Israel. It could lead to heavy civilian casualties on the Palestinian side and trigger strong international criticism, as was the case during one that killed hundreds of Palestinians in 2009. Israeli troops would also be at much greater risk if they enter Gaza's crowded urban landscape, home to 1.8 million people, especially for a long-term presence.
Tal Russo, a former general who retired last year as head of Israel's southern command, said a ground offensive did not guarantee success. "There is no such concept as 'decisive,' and that needs to be understood," he told Channel 10 TV.
Israeli security officials say they have prepared different scenarios inside Gaza, ranging from a quick pinpoint operation to a full re-occupation of the seaside strip. Israel withdrew from Gaza in 2005.
In the first indication that cease-fire efforts were underway, the office of Egyptian President Abdel-Fattah el-Sissi said he held "extensive contacts with all active and concerned parties" to end the fighting.
It said the two sides discussed the "critical conditions and the need to stop all military action, and to stop the slide" toward more violence. It called on Israel to protect Palestinian civilians.
Egypt negotiated a cease-fire that ended the 2012 fighting, but the situation has changed since then. At the time, Egypt was led by the Muslim Brotherhood, a regional movement that includes Hamas. Following a military coup last year, el-Sissi was elected president, and the new government is far more hostile toward Hamas.
U.N. Secretary-General Ban Ki-moon said he spent Wednesday calling Netanyahu, Palestinian President Mahmoud Abbas, el-Sissi and other regional leaders to push the two sides toward a cease-fiore
"This is one of the most critical tests the region has faced in recent years," Ban told a news conference. "Gaza is on a knife-edge. The deteriorating situation is leading to a downward spiral which could quickly get beyond anyone's control."
In Washington, the State Department said Kerry spoke by phone with Netanyahu and planned to talk to Abbas to urge both sides to de-escalate the crisis.
Netanyahu confirmed he spoke to Kerry, Ban and German leader Angela Merkel, but gave no indication the offensive would stop.
"Today I spoke with several world leaders. I appreciated their expressions of strong support for our right and our duty to defend ourselves, and this is what we will continue to do," he said.
If the offensive drags on, Netanyahu could find himself under increased pressure to halt it, especially if the civilian death toll mounts.
The airstrikes have demolished dozens of buildings. Among the latest dead were an 80-year-old woman, an 11-year-old girl, a 14-year-old boy and two young children. Israel has accused militants of endangering civilians by using homes and other civilian buildings for cover.
Mohammed al-Nuasrah of the Maghazi refugee camp in central Gaza described a scene of horror after an airstrike flattened a nearby home.
"Four people from the family died, and we're sitting looking for the remains of the kids. One is 3 and one is 4 years old," he said. "These children were just sleeping in their beds. What crime did they commit? Only God can judge you, Israel."
In a statement broadcast on Al-Jazeera, Hamas' exiled leader, Khaled Mashaal, called on all Palestinians to resist Israel and urged the international community to put pressure on Israel.
"Yes, our enemy is stronger than us, but we are up to the task of facing them, God willing," he said. "We do not threaten or promise. Our right is to defend our lives."
The longer range of the rockets fired from Gaza has disrupted life across southern and central Israel, where people have been forced to remain close to home, and kindergartens and summer camps have closed.
Besides firing toward Israel's two largest cities of Tel Aviv and Jerusalem, Hamas also launched a rocket that reached the city of Hadera for the first time. The city, more than 100 kilometers (60 miles) north of Gaza, was struck in 2006 by missiles fired by Hezbollah guerrillas in Lebanon.
"We got it from both directions," said Maayan From, a 25-year-old Hadera resident. "Our enemies have developed, and it is getting scary."
In the West Bank, Abbas accused Israel of committing "genocide" due to the mounting civilian death toll and said it raised questions about Israel's commitment to peace.
Tensions have been rising since the June 12 kidnapping of three Israeli teenagers in the West Bank. Israel accused Hamas of being behind the abductions but provided no proof.
Israel then cracked down on the group's members in the West Bank and arrested hundreds of people. Hamas, which controls Gaza, responded by stepping up rocket fire.
The situation deteriorated last week after the bodies of the three were found, followed a day later by the abduction in Jerusalem of a Palestinian teenager who was found burned to death in what Palestinians believe was a revenge attack. Six Jewish Israelis were arrested in the killing.
Adding to the tension, a 15-year-old Palestinian-American cousin of the slain teenager was beaten by Israeli police at a protest. Israel's Justice Ministry said one of the officers would face criminal charges.
Associated Press writers Mohammed Daraghmeh in Ramallah, West Bank, Najib Jobain in Gaza City, Gaza Strip, Sarah El Deeb in Cairo, Aya Batrawy in Dubai, Edith M. Lederer at the United Nations, and Ian Deitch and Yousur Alhlou in Jerusalem contributed to this report.