GAZA — Israeli airstrikes against Hamas facilities in Gaza continued for a second day on Sunday and the death toll rose to more than 280 as Israel retaliated for rocket fire from the area with its most severe campaign against Palestinian militants in decades.

The Palestinian groups again launched barrages of rockets and mortars into Israel on Sunday, extending their reach further than ever before, and the Israeli government approved the emergency call up of thousands of army reservists in preparation for a possible ground operation.

Speaking before the weekly cabinet meeting in Jerusalem, Israeli Defense Minister Ehud Barak said the army “will deepen and broaden its actions as needed” and “will continue to act in Gaza.”

Among the 30 or more targets hit Saturday night and early Sunday was the main security compound and prison in Gaza City known as the Saraya; metal workshops throughout Gaza; Hamas military posts; and the house of a chemistry professor from Gaza’s Islamic University. The Hamas-owned Al-Aqsa television station was also struck, as was a mosque that the Israeli military said was housing armed men and was being used as a terrorist operation center.

Palestinian officials said that most of the dead in Gaza were security officers for Hamas, including two senior commanders, and that at least 600 people had been wounded in the attacks.

The prime minister of Israel, Ehud Olmert, said on Sunday that “the patience, determination and stamina” of the residents of Israelis would, in the end, determine the success of the military and diplomatic campaign against Hamas.

Two rockets fell in the vicinity of the major Israeli port city of Ashdod, almost 25 miles north of Gaza, a military spokeswoman said. Others landed in the coastal city of Ashkelon. Several Israelis were lightly wounded by shrapnel. The hundreds of thousands of Israeli citizens now within rocket range have been instructed by the authorities to stay close to protected spaces and an emergency has been declared.

Israeli military officials said that the airstrikes, which began on Saturday morning, were the start of what could be days or even months of an effort to force Hamas to end its rocket barrages into southern Israel.

After the initial airstrikes, dozens of rockets were fired into southern Israel sending thousands of Israelis into bomb shelters. One man was killed on Saturday in the town of Netivot, the first death from rocket fire since it intensified a week ago.

A number of governments and international officials, including leaders of Russia, Egypt, the European Union and the United Nations, condemned Israel’s use of force and also called on Hamas to end the rocket fire. But in strong terms, the Bush administration blamed Hamas for the violence and demanded that it stop firing rockets.

Early Sunday morning in New York, the United Nations Security Council issued a statement expressing concern about the escalation of the conflict and calling on both parties for an immediate end to all violence. The statement came after envoys of the 15-member council met for over four hours in a closed session, Reuters reported.

A military operation had been forecast and demanded by Israeli officials for weeks, ever since a rocky cease-fire between Israel and Hamas fully collapsed a week ago, leading again to rocket attacks in large numbers against Israel and isolated Israeli operations here.

Still, there was a shocking quality to Saturday’s attacks, which began in broad daylight as police cadets were graduating, women were shopping at the outdoor market, and children were emerging from school.

The center of Gaza City was a scene of chaotic horror, with rubble everywhere, sirens wailing, and women shrieking as dozens of mutilated bodies were laid out on the pavement and in the lobby of Shifa Hospital so that family members could identify them. The dead included civilians, including several construction workers and at least two children in school uniforms.

By afternoon, shops were shuttered, funerals began and mourning tents were visible on nearly every major street of this densely populated city.

The leader of the Hamas government in Gaza, Ismail Haniya, said in a statement that “Palestine has never witnessed an uglier massacre.” Later, in a televised speech, he vowed to fight Israel. “We say in all confidence that even if we are hung on the gallows or they make our blood flow in the streets or they tear our bodies apart, we will bow only before God and we will not abandon Palestine,” he said.

In Damascus, Syria, Hamas’s supreme leader, Khaled Meshal, said in an interview with Al Jazeera television that he was calling for a new Palestinian intifada against Israel, including the resumption of suicide attacks within Israel for the first time since 2005. Hamas, he said, had accepted “all the peaceful options, but without results.”

“We wanted to attack military targets while the terrorists were inside the facilities and before Hamas was able to get its rockets out that were stored in some of the targets,” said a top Israeli security official, briefing a group of reporters by telephone on condition of anonymity.

“Right now, we have to hit Hamas hard to stop the launching,” he added. “I don’t see any other way for Hamas to change its behavior. Hamas is not just a terrorist organization. It actually rules Gaza and is well supported by Iran with some of its leadership in Syria.”

Hamas had in recent weeks let it be known that it doubted Israel would engage in a major military undertaking because of its coming elections. But in some ways the elections have made it impossible for officials like Mr. Barak not to react, because the public has grown anxious and angry over the rocket fire, which while causing no recent deaths and few injuries is deeply disturbing for those living near Gaza.

Israeli officials said that anyone linked to the Hamas security structure or government was fair game because Hamas was a terrorist group that sought Israel’s destruction. But with work here increasingly scarce because of an international embargo on Hamas, young men are tempted by the steady work of the police force without necessarily fully accepting the Hamas ideology. One of the biggest tolls on Saturday was at a police cadet graduation ceremony in which 15 people were killed.

Spokesmen for Hamas officials, who have mostly gone underground, called on militants to seek revenge and fight to the last drop of blood. Several compared what was happening to the 2006 war between Israel and the Lebanese militia Hezbollah, when Israel reacted to the capture and killing of soldiers along its northern border with air raids, followed by a ground attack. Hezbollah is widely viewed as having withstood those assaults and emerged much stronger politically.

The Arab League initially called an emergency meeting for Sunday in Cairo with all the foreign ministers from the member states, but later postponed it to Wednesday to give ministers time to respond.

Governments that dislike Hamas, like Egypt’s, Jordan’s and the Palestinian Authority in the West Bank, are in a delicate position. They blame Hamas for having taken over Gaza by force 18 months ago in the aftermath of its election victory in the Palestinian Parliament, and they oppose its rocket fire on Israeli towns and communities.

But the sight of scores of Palestinians killed by Israeli warplanes outraged their citizens, and anti-Israel demonstrations broke out across the region.

President Mahmoud Abbas of the Palestinian Authority angrily condemned the Israeli airstrikes. Egypt, worried about possible efforts by Palestinians to enter the country, has set up machine guns along the Gaza border. But on Saturday it temporarily opened the Rafah border crossing in order to allow the wounded to be brought to Egyptian hospitals.

In the West Bank and in some Arab parts of Jerusalem and Israel, Palestinians threw stones, causing some injuries.

Hamas is officially committed to Israel’s destruction, and after it took over Gaza in 2007, it said it would not recognize Israel, honor previous Palestinian Authority commitments to it or end its violence against Israelis.

Israel, backed by the United States, Europe, Egypt and the Palestinian Authority, has sought to isolate Hamas by squeezing Gaza economically, a policy that human rights groups condemn as collective punishment. Israel and Egypt, which control routes into and out of Gaza, have blocked nearly all but humanitarian aid from going in.

The result has been the near death of the Gazan economy. While enough food has gone in to avoid starvation, the level of suffering is very high and getting worse each week, especially in recent weeks as Israel closed the routes entirely for about 10 days in reaction to daily rocket fire.

Opening the routes to commerce was Hamas’s main goal in its cease-fire with Israel, just as ending the rocket fire was Israel’s central aim. But while rocket fire did go down drastically in the fall to 15 to 20 a month from hundreds a month, Israel said it would not permit trade to begin again because the rocket fire had not completely stopped and because Hamas continued to smuggle weapons from Egypt through desert tunnels. Hamas said this was a violation of the agreement, a sign of Israel’s real intentions and cause for further rocket fire. On Wednesday, some 70 rockets hit Israel over 24 hours, in a distinct increase in intensity.