Israeli Airstrikes Slam Gaza It was the heaviest bombardment in Gaza in three weeks.

 -- Israel slammed Gaza with a barrage of airstrikes overnight in what was the heaviest bombardment in the three-week conflict. At least 60 died in the strikes in Gaza overnight.

Symbols of Hamas control came under fire, including TV headquarters, government offices and the home of a top leader. Israel said it targeted more than 70 sites and hit 10 “terror operatives.”

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The Gaza Strip’s only power plant was struck by a tank shell, hitting a fuel tank and causing the plant to shut down, the head of the power station told ABC News. Fire burned following the attack, with heavy smoke rising over Gaza City. Engineer Fatahi Khalil, from the electricity company, confirmed to ABC News that it will take a year to fix the power plant. The damage will be assessed at a later time, he said.

The pounding came hours after Israeli Prime Minister Benjamin Netanyahu warned in a televised speech of a "prolonged" campaign in Gaza.

Hamas also signaled defiance. Ismail Haniyeh, the Hamas leader whose house was struck in an airstrike early Tuesday, said in a statement that "destroying stones will not break our determination."

The tough words by both sides came amid mounting international appeals for an unconditional cease-fire.

However, Hamas has said it will not stop fighting until it wins international guarantees that a seven-year-old border blockade of Gaza will be lifted. Israel said its troops will not leave Gaza until they have demolished several dozen Hamas military tunnels under the Gaza-Israel border. Late Monday, Netanyahu signaled that Israel is intensifying its air and ground campaign.

The overall Gaza death toll rose past 1,100, according to the Palestinian health ministry, with another 6,500 injured.

Israel says it has lost 53 soldiers, along with two civilians and a Thai worker.

The Associated Press contributed to this report.