GAZA CITY (CNN) -- The death toll from a weekend of Israeli airstrikes on Gaza has topped 300, Palestinian medical sources said Monday as a third day of air raids hit the Hamas-ruled territory.
Fires rage overnight in Gaza, where Israel has been bombing what it says are Hamas targets. more photos »
Another 650-plus people have been wounded in the strikes, the sources said.
The U.N. Security Council has called for an immediate end to the airstrikes, which began Saturday. But Israel says its objective is to stop an ongoing stream of rockets fired by Hamas militants into southern Israel, and Prime Minister Ehud Olmert told Cabinet ministers Sunday that the situation "is liable to continue for some time."
Hamas, the Islamic militant group that controls Gaza, pledges it will defend its land and people in the face of what it calls continued Israeli aggression. Each side blames the other for violating an Egyptian-brokered cease-fire, which formally expired Friday, December 19, but in reality had been weakening for months. Watch as Gaza endures third day of attacks »
Israel has struck more than 300 Hamas targets since Saturday, its military said. The Israel Defense Forces said Monday that more than 150 rockets have been launched into Israeli territory from Gaza since the campaign began. One of those hit a home in southern Israel on Saturday, killing one man inside. Watch parts of Gaza reduced to rubble »
Palestinian security and medical sources said airstrikes hit the Jebaliya refugee camp in Gaza early Monday, and a home near Hamas leader Ismail Haniya's residence was hit overnight. Hamas security sources said that raid targeted the home of a senior leader in the group's military wing.
The Jebaliya raid left five children dead in a home that was damaged when a nearby mosque was targeted, said Dr. Mu'awiya Hassanein. The Israeli military had no immediate comment on that claim.
And a few minutes after midnight, an Israeli F-16 fired rockets into at least one building at the Islamic University of Gaza, a Gaza-based journalist at the scene -- whose name was withheld for security reasons -- told CNN. There were no immediate reports of casualties from that strike, which the IDF said targeted "a center for weapon research and development."
The Palestinian television station Ramattan showed firefighters trying to put out a fire at a building identified by the Palestinian network as part of the university, while others sifted through large piles of debris and rubble. Read reactions to Israel's strike on Gaza »
"There was a loud series of explosions ... the entire apartment I'm in was shaking," said Sami Abdel-Shafi, a Palestinian business consultant in Gaza City. "It was scary and a very disappointing position to be in for the 'nth' time."
An Israeli military statement said the targets of the raid were "buildings that were used as meeting places for senior leaders of Hamas." Watch an ambassador say Israel is only defending itself »
"One of the structures struck housed explosives laboratories that were an inseparable part of Hamas' research and development program, as well as places that served as storage facilities for the organization," the IDF statement said. "The development of these weapons took place under the auspices of senior lecturers who are activists in Hamas. Among the weapons that have been developed and manufactured at this site are Qassam rockets."
There was no immediate response from Hamas to the IDF statement.
CNN's Kevin Flower and Elise Labott contributed to this report.
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Palestinian-Israeli conflict area and War on Terrorism around the Gaza strip
Israel has launched with at least 30 simultaneous missiles strikes on Hamas installations in Gaza City, causing heavy damage. F-16 fighters targeted security compounds in the city’s centre.

The “massive” air strikes on Saturday have claimed at least 220 lives, including Gaza police chief Maj. Gen. Tawfiq Jaber. More than 700 were injured, while others were still buried under the rubble, according to Health Ministry officer Moawiya Hassanain. Gaza City hospitals, including Shifa Hospital, Gaza’s main treatment center, are crowded with wounded victims. In response thirteen rockets and mortar shells had also hit southern Israel on Friday, damaging an unoccupied house. 

Meanwhile, Hamas declared  it would retaliate, by launching rocket attacks on and sending suicide bombers to Israel. “Hamas will continue the resistance until the last drop of blood,” warned Hamas spokesman Fawzi Barhoum. Palestinian President Mahmoud Abbas, Hamas’ rival,  says he “condemns this aggression” and calls for restraint.
Hamas-run Gaza Strip.

Qassam rocket fired from the Gaza Strip hits southern Ashkelon in Israel.

When the Egyptian-mediated truce terminated last week, Israel warned of their potential to launch a major offensive on Gaza, amid senior leaders’ call to topple Hamas. “I will not hesitate to use Israel’s strength to strike at Hamas and Islamic Jihad,” Prime Minister Ehud Olmert announced on Thursday, issuing a dire warning that ”tens of thousands of children and innocents” would be at risk “as a result of Hamas’ actions.” Defense Minister Ehud Barak says Israel has temporarily opened some border crossings Friday to allow humanitarian aid into the Gaza Strip in response to the international community’s pleas.

Two hours after IAF missiles targeted Hamas installations in the Gaza Strip, Palestinian gunmen launched on Saturday a massive attack with Qassam rockets on Israeli territory. Seven struck Ashkelon, killing one person, while another suffered serious injuries, and four others were moderately wounded when their house was hit. They were rushed to the Soroka hospital in Beersheva. 

According to the IDF, Hamas militants had further launched more than 110 rockets since Saturday, IDF says. Meanwhile, a Palestinian Ambassador Riyad Mansour has called on the United Nations to condemn the deadly violence. "There is no justification for punishing 1.5 million in the Gaza Strip because of the actions of a few. We hope we don't fail in having a reaction from the Security Council tonight," he said. Dr Moawiya Hassanein has said "we have counted 271 dead and 620 wounded since Saturday."

The 2008–2009 Israel–Gaza conflict, referred to as "Operation Cast Lead" (מבצע עופרת יצוקה - also known as "Operation Solid Lead") by the Israel Defense Forces (IDF), is an Israeli air strike operation launched on December 27, 2008 at 11:30 am local time (9:30 am UTC) against Hamas targets in the Gaza Strip. Israeli officials justified the offensive as a retaliation against daily Palestinian Qassam rocket and mortar fire on Israel's southern communities.