In Saturday's fighting, Israeli aircraft pounded militants' weapons storage facilities and underground rocket launching sites, and went after rocket squads more aggressively.
Militants, undaunted, have unleashed some 500 rockets against the Jewish state.
Hamas claims that Israeli intelligence is based on a network of collaborators in Gaza. Officials said two Palestinians have been executed by Hamas' military wing for allegedly providing Israel with sensitive information. One man was shot twice in the head. Another body was tossed into a garbage bin with a gunshot wound to the head.
The violence has threatened the Mideast with a new war. At the same time, revolts against entrenched regional regimes have opened up new possibilities for Hamas. Islamists across the Mideast have been strengthened, bringing newfound recognition to Hamas, which had previously been shunned by the international community because of its refusal to recognize Israel and renounce violence.
A high-level Tunisian delegation, led by Foreign Minister Rafik Abdessalem, drove that point home with a visit to Gaza on Saturday. The foreign minister's first stop was the still-smoldering ruins of the three-story office building of Gaza's prime minister, Ismail Haniyeh of Hamas.
"Israel has to understand that there is an international law and it has to respect the international law to stop the aggression against the Palestinian people," Abdessalem told the AP during a tour of Gaza's main hospital. He said his country was doing whatever it can to promote a cease-fire, but did not elaborate.
It was the first official Tunisian visit since Hamas's violent 2007 takeover of the territory. The West Bank is governed by Palestinian President Mahmoud Abbas. Egypt's prime minister visited Gaza on Friday and a Moroccan delegation was due on Sunday, following a landmark visit by Qatar's leader last month.
Israel had been incrementally expanding its operation beyond military targets but before dawn on Saturday it ramped that up dramatically, hitting Hamas symbols of power.
Israeli defense officials, speaking on condition of anonymity to discuss confidential decisions, said military chief Lt. Gen. Benny Gantz personally ordered the scope of the airstrikes to be increased.
Haniyeh's three-story office building was flattened by an airstrike that blew out windows in neighboring homes. He was not inside the building at the time.
Another airstrike brought down the three-story home of a Hamas commander in the Jebaliya refugee camp near Gaza City, critically wounding him and injuring other residents of the building, medics said.
Missiles smashed into two small security facilities and the massive Hamas police headquarters in Gaza City, setting off a huge blaze that engulfed nearby houses and civilian cars parked outside, the Interior Ministry reported. No one was inside the buildings.
The Interior Ministry said a government compound was also hit while devout Muslims streamed to the area for early morning prayers, although no casualties were reported.
Air attacks knocked out five electricity transformers, cutting off power to more than 400,000 people in southern Gaza, according to the Gaza electricity distribution company. People switched on backup generators for limited electrical supplies.
In southern Gaza, aircraft went after underground tunnels militants use to smuggle in weapons and other contraband from Egypt, residents reported. A huge explosion in the area sent buildings shuddering in the Egyptian city of El-Arish, 45 kilometers (30 miles) away, an Associated Press correspondent there reported.
The Israeli military said more than 950 targets have been struck since the operation began.
On Saturday, more than 120 rockets slammed into Israel, causing damage to houses. About 10 Israelis were injured lightly, among dozens of others wounded since the start of the operation.
Despite the violence, Egyptian-led diplomacy was underway to bring an end to the fighting.
Egyptian President Mohammed Morsi was meeting the leaders of Turkey and Qatar Saturday as well as Hamas leader Khaled Meshal to discuss details of a proposed cease-fire.
The Arab League also met Saturday to consider sending its chief Nabil Elaraby and a team of foreign ministers to Gaza in the coming two days to assess the situation and respond to humanitarian needs there, according to a draft memorandum obtained by the AP.
Turkish Prime Minister Recep Tayyip Erdogan told reporters Saturday that during discussions with Obama and Russian President Vladimir Putin late Friday, he suggested that Turkey, Egypt, the United States and Russia help broker a simultaneous cease-fire between Israel and Hamas.
"It would be good if we could work on it rapidly to solve the matter within 24 hours, because the death toll is mounting," he said.
Goldenberg reported from Jerusalem. Associated Press writers Karin Laub in Gaza City, Matthew Daly in Washington and Aya Batrawy in Cairo contributed reporting.
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