GAZA CITY (CNN) -- Israeli jets pounded Hamas targets in Gaza for a third day Monday, continuing an operation that Palestinian security sources said has killed more than 270 people.
Hamas militants launched more rockets into Israel on Sunday. Israel has said its airstrikes are a necessary self-defense measure after repeated rocket attacks from Gaza into southern Israel.
Israeli Foreign Minister Tzipi Livni told CNN on Sunday that the airstrikes will continue "until we have a change on the ground" and that Israel has not ruled out a ground war in Gaza.
"Israel targets only military targets and places in which we know Hamas members are," Livni said.
"Unfortunately, in this kind of attack, there are some civilian casualties. But Israel took all the necessary actions to warn the civilians before the attacks to leave the places they know that Hamas stays."
Israeli ground troops and tanks were deployed around Gaza on Sunday. There is no indication of a ground operation inside Gaza, but a senior military official said troops around Gaza will "be activated if needed." Watch an ambassador say Israel is only defending itself »
Israel will call up 7,000 reserve soldiers, Defense Minister Ehud Barak said during Sunday's Cabinet meeting. He told ministers he planned to present the measure to two Knesset committees, which must approve the action.
Early Monday, an Israeli jet bombed part of 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.
Video footage from Palestinian TV network Ramattan showed firefighters trying to extinguish a fire at a building the network identified as part of the university.
When CNN asked Israel Defense Forces about the incident, the IDF sent a statement that said the site "housed explosives laboratories that were an inseparable part of Hamas' research and development program," and that weapons development there "took place under the auspices of senior lecturers who are activists in Hamas."
The IDF and the Israeli Air Force struck "buildings that were used as meeting places for senior leaders of Hamas," the statement said.
In Jabalya, a mosque and a family home were hit by rockets early Monday, according to Hamas security sources. Palestinian medical officials said five children died and two survived. Footage from the scene showed the two surviving girls being taken into an ambulance.
Palestinian security sources said Sunday that at least 277 people, most of them Hamas militants, have been killed and hundreds more wounded.
On Sunday, black plumes of smoke rose above Gaza City as makeshift ambulances screamed down rubble-strewn streets, taking wounded Palestinians to hospitals already crowded with hundreds of patients injured over the weekend.
Terrified people huddled in their basements for safety, with few venturing outside, said Dr. Eyad El-Sarraj, a psychiatrist who runs Gaza's mental health program.
"The children are terrified," El-Sarraj said. "Adults are unable to provide them with security or warmth. Hospitals are stretched out of the limits. We need blood and medicine and surgical equipment."
The U.N. Security Council ended a four-hour emergency meeting Sunday with a call for an immediate halt to hostilities and a re-opening of border crossings to allow humanitarian supplies to reach Gaza.
The Palestinians' U.N. envoy said if Israel does not halt attacks within 48 hours, Arab delegations will demand stronger action from the Security Council.
Israel gave in to requests from the Red Cross and others to allow 16 trucks loaded with fuel, food and medical supplies into Gaza through the Kerem Shalom crossing Sunday morning. Egypt sent 20 ambulances to its border with Gaza, an Egyptian official said.
The Red Cross and World Food Program trucks, which carried rice, wheat and medical supplies, were the first deliveries allowed by Israel since 80 trucks moved through Friday after Israel opened three border crossings.
More than 110 Hamas rockets have been launched into Israel by Hamas militants since Saturday morning, an Israel Defense Forces spokesman said. An Israeli man died when a rocket slammed into a home Saturday, IDF said.
An Israeli police spokesman said that one rocket landed north of Ashkelon, which sits about 6 miles (10 kilometers) north of the Gaza border. The city has been a frequent target of missiles launched from Gaza.
Gaza City's main police station and jail were hit by Israeli missiles Sunday morning, according to a Gaza-based journalist.
At least two people were killed when a missile struck the Seraya compound, which houses various Hamas military organizations in central Gaza City. Another two people were killed when an airstrike hit a vehicle.
Missiles also hit near the Beit Hanoun City Hall, according to a reporter there, and Palestinian sources said Israeli bombs fell on the Palestinian side of the Rafah tunnels on the Egyptian border with southern Gaza.
An Israeli army spokesman confirmed the airstrike. He said it targeted 40 tunnels on the border, which he said Hamas uses to smuggle weapons into Gaza.
Two tunnels were hit by missiles, eyewitnesses said, and others collapsed. Two people were killed.
An Egyptian soldier was killed and two other troops were wounded by Palestinians who opened fire at the Rafah border crossing, Egypt's state-run news agency reported, citing security sources.
Palestinians began trying to cross over into Egypt through a hole in the wall after the bombing, witnesses said, but Egyptian police and Hamas gunmen began firing in an attempt to stop them.
More than 40 airstrikes were carried out Sunday, the Israeli army said. An IDF spokesman said Sunday that Israel had struck 210 Hamas targets since Saturday morning.
The Security Council issued a brief press statement, which fell short of the resolution that the Palestinians requested.
The statement expressed "serious concern at the escalation of the situation in Gaza," but it did not single out Israel or Hamas when it called for "an immediate halt for all violence."
Israel's ambassador to the U.N., Gabriela Shalev, responded that her country was only defending itself from Hamas rocket attacks.
"The last days were so bad that we had to say, and did say, 'Enough is enough,' " Shalev said. "The only party to blame is the Hamas."
Hamas, however, vowed to retaliate, saying Israel had violated an Egyptian-brokered cease-fire intended to stem violence in the region.
"We will stand up, we will defend our own people, we will defend our land and we will not give up," senior spokesman Osama Hamdan said. Read reactions to Israel's strike on Gaza »
The U.S. ambassador to the U.N., Zalmay Khalilzad, supported Israel's contention that it was up to Hamas to stop the violence.
"Israel has the right to self-defense and nothing in this press statement should be read as anything but that," Khalilzad said.The United States has cautioned Israel, however, to avoid civilian casualties. Israeli leaders maintain they are attempting to do so.