GAZA CITY, Gaza Strip — Israel destroyed the headquarters of Hamas’ prime minister and blasted a sprawling network of smuggling tunnels in the southern Gaza Strip on Saturday, broadening a blistering four-day-old offensive against the Islamic militant group even as diplomatic efforts to broker a cease-fire appeared to be gaining steam.

Hamas officials said a building used by Hamas for broadcasts was bombed and three people were injured. The injured were from Al Quds TV, a Lebanon-based television channel. The building is also used by foreign news outlets including Germany’s ARD, Kuwait TV and the Italian RAI and others.

The Israeli military spokesman was not immediately aware of the strikes but said they were investigating.

In neighboring Egypt, President Mohammed Morsi hosted leaders from Hamas and two key allies, Qatar and Turkey, to seek a way to end the fighting.

“There are discussions about the ways to bring a cease-fire soon, but there are no guarantees until now,” Morsi said at a news conference. He said he was working with Turkey, Arab countries, the U.S., Russia and western European countries to halt the fighting.

Israel launched the operation Wednesday in what it said was an effort to end months of rocket fire out of the Hamas-ruled territory. It began the offensive with an unexpected airstrike that killed Hamas’ powerful military chief, and since then has relentlessly targeted suspected rocket launchers and storage sites.

In all, 48 Palestinians, including 15 civilians, have been killed and more than 400 civilians wounded, according to medical officials.

Three Israeli civilians have been killed and more than 50 wounded.

Israeli military officials expressed satisfaction with their progress today, claiming they have inflicted heavy damage to Hamas.

“Most of their capabilities have been destroyed,” said Maj. Gen. Tal Russo, Israel’s southern commander.

Asked whether Israel is ready to send ground troops into Gaza, he said: “Absolutely.”

“Most of their weapons are stored in civilian’s homes, they launch rockets from residential areas. We do not want to hit civilians in Gaza but we do want to hit the hornets’ nest of terror in Gaza,” he said.

Footage released today by the Islamic Jihad showed rockets being fired from a hidden bunker in a residential area of Gaza.

Israel’s Deputy Foreign Minister Danny Ayalon told channel 1 TV that “Hamas is committing a double war crime, they are firing rockets at Israeli civilians while using Palestinian civilians as human shields.”

The White House said President Barack Obama was also in touch with the Egyptian and Turkish leaders. The U.S. has solidly backed Israel so far.

Speaking on Air Force One, deputy national security adviser Ben Rhodes said that the White House believes Israel “has the right to defend itself” against attack and that the Israelis will make their own decisions about their “military tactics and operations.”

Despite the bruising offensive, Israel has failed to slow the barrages of rockets from Gaza.

The Israeli military said 160 rockets were launched into Israel on Saturday, raising the total number to roughly 500 since the fighting began.

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