(ABC News) -- In the early hours of Saturday morning, Israel's Air Force reduced the headquarters of the militant group Hamas to rubble. It was one of several Hamas buildings and homes targeted, part of Israel's continuing effort to destroy the group's command and control structure as speculation mounts over an Israeli ground invasion.
The Israel Defense Forces released aerial drone video of the attack on the government building, the seat of Hamas Prime Minister Ismail Hanniyeh. Israeli warplanes have also struck the main police station, the interior ministry and the homes of top Hamas leaders.
Raw video: Israel fires rockets from 'Iron Dome'
As of Saturday morning, almost 900 "terror sites" had been targeted by Israel, including weapons caches and rocket launching sites. Around 600 rockets have been fired into Israel by Hamas and other militant groups, around a third of which were intercepted by the Iron Dome anti-missile system, according to the Israeli military.
Raw video: Israel shoots down Tel Aviv-bound rocket
The loud thud of Israeli missiles hitting Gaza and the buzz of drones overhead were consistent on Saturday, as Israeli tanks and troops massed on the border in preparation of a ground invasion. Israeli media also reported that 20,000 reservists have been called up.
"We are preparing for any possibility, a ground invasion is a possibility although it hasn't been decided at this point," said IDF spokeswoman Lieutenant Colonel Avital Liebovich. "We are ready to continue this operation "Pillar of Defense "until the peace and quiet and normality will return."
On Friday, Jerusalem was targeted for the first time in this escalation by militants in Gaza. A rocket landed around ten miles south near the West Bank Israeli settlements of Gush Etzion. And for the second day, sirens sounded in Tel Aviv as a rocket landed off the coast.
Three Israelis were killed Thursday by a rocket attack in the southern town of Kiryat Malachi. As of Saturday morning 39 Palestinians had been killed, among them more than half were civilians, according to Gaza health officials.
"Up until now we can say the situation is stable," Dr. Ayman al-Sahbani, the head of the emergency unit at Gaza's main al-Shifa hospital, said on Friday. "If it continues, we can't [cope]. Of course we can't. We hope to stop the [Israeli] aggression."
Egyptian Prime Minister Hisham Qandil visited the strip for three hours Friday morning, raising hope a ceasefire would be brokered. Qandil and the Egyptian President Mohammed Morsi, are both from the Muslim Brotherhood, of which Hamas is an offshoot. They have the delicate task of trying to coordinate between Hamas, Israel and the United States.
"What I am witnessing in Gaza is a disaster and I can't keep quiet," Qandil said, "The Israeli aggression must stop." Israel says this operation, dubbed "Pillar of Defense," is the result of the rockets that regularly fly into southern Israel from Gaza. This operation started when Israel assassinated the top commander of Hamas' military wing, Ahmed Jabari.
"As long as Israel keeps killing us, we will keep defending ourselves by any means possible," the spokesman of Islamic Jihad, Daoud Shahab said in an interview. "If Israel stops its aggression, we are ready to stop firing the rockets."
In Washington, the Obama administration reiterated its view that Israel has the right to defend itself.
"It's a matter of the international community and particularly regional states with influence to do what they can to make clear to Hamas that this is not benefiting the cause of the Palestinian people, and it's certainly not benefiting the cause of regional stability," said State Department spokesperson Victoria Nuland.