The Israeli military on Thursday shelled the main United Nations aid compound in Gaza, struck a building that houses foreign news organizations, and caused a fire at a hospital. The attacks sparked global condemnation even as efforts to reach a cease-fire continued.

Later in the day, Hamas struck the Israeli city of Beersheba with a salvo of Qassam rockets, injuring five people, two of them seriously.

The Israeli strikes on what political officials said were unintended targets in the Gaza campaign underscore what some analysts see as a furious drive by the Israeli Defense Forces (IDF) to achieve as many last-minute blows to Hamas as possible before a cease-fire is reached. And at this stage of the war, fissures are emerging within the Israeli civilian and military leadership.

"It's the final push to make Hamas understand, either they make a decision for a cease-fire, or it will be difficult to survive," says Shmuel Rosner, a leading opinion maker and journalist. "They need to show seriousness so Hamas doesn't interpret Israel's waiting of the last few days as reluctance to continue the operation."

While Ehud Barak, Israel's defense minister, apologized to UN Secretary-General Ban Ki Moon for Israel's strike on their Gaza headquarters, Prime Minister Ehud Olmert took a different approach. He said the building had been used by Palestinian militants to strike Israeli forces.

Mr. Olmert, quoting a senior IDF officer, said Israel's troops opened fire on militants inside the compound shot antitank weapons and machine guns. "It is absolutely true that we were attacked from that place," he said.

Those two points provide a window into the differences that have developed at the top of the Israel political structure, run by an unlikely troika of Olmert, Mr. Barak and Foreign Minister Tzipi Livni – none of whom are allied.

With an election set for Feb. 10, the political rivals have become even more assertive in claiming their share of the credit for the war.

Ms. Livni, who is running to succeed Olmert, reportedly favors a unilateral pullback even without a cease-fire, according to media reports. A swift pullback would minimize risks to Israeli soldiers as well as the chances of a giving Hamas an opportunity to score any parting blows. A quick withdrawal would also improve Israel's position with its Western allies, which is progressively eroding as damage and death tolls mount.

"She is afraid of a mess up," says Gideon Doron, a political science professor at Tel Aviv University. "The longer you stay there, the higher the likelihood of a soldier getting hurt. That's bad for the ruling party."

Barak, who has got a boost from the polls for leading the war effort, reportedly supports a swift "humanitarian" cease-fire and the Egyptian efforts to reach a truce with Hamas. He would also like to wrap up the fighting and show a willingness to pursue peace to bolster his position among in his pro-peace Labor Party.

Olmert, who reportedly supports continuing the operation, is a lame duck prime minister and is free of his colleagues' political calculations. Mr. Doron says he's concerned about his legacy and would like to be remembered as the leader who squashed Hamas.

But meanwhile in Gaza, the war moved into one of its most deadly days amid some of the heaviest Israeli shelling on Thursday. Israel's military chief of staff told a parliamentary committee Tuesday that although Hamas has been dealt a serious blow, "we still have work to do."

In the crosshairs are senior Hamas figures who have gone underground, including Mahmoud az-Zahar – whose home was hit by the Israeli air force late Wednesday night. Hamas Interior Minister Saeed Seyyam was also killed Thursday. Mr. Seyyam controlled Hamas police and security forces of about 13,000 men, many of whom were directly involved with fighting.

Many observers say that IDF strategists have a short-list of targets they want to strike before a cease-fire. The Israel defense establishment, they say, is loath to slow down and give the impression that it's tired or is lacking in the will to continuing fighting Hamas.

But Israel missile strikes drew even sharper international condemnation on Thursday, in particular from the UN Secretary-General, Ban Ki Moon, who is in Israel trying to bring about a cease-fire that would end Israel's attacks on Gaza and the continued launch of rockets at Israel by Hamas militants.

Into the afternoon Thursday, the UN headquarters in Gaza, where some 700 Palestinian civilian had sought shelter, was still burning out of control, several hours after it was hit, forcing the suspension of major aid operations in the coastal territory. The chief of operations there said there wasn't enough water to douse the flames, a result of Gaza's battered infrastructure in the 20-day war with Israel.

"The warehouses are burning down, the fire is spreading, and we're very concerned," says John Ging, the director of operations in Gaza for UN Relief Works Agency (UNRWA), the UN's main arm for aid to Palestinians.

"There's a shortage of water and that's why it's spreading. All the food, medicine, and humanitarian aid we have to distribute in Gaza are stored here," Ging adds.

The solution is to "stop the shooting, respect the UN, and then we can start to rebuild. Our compound is falling apart before my eyes! There are a million-and-half people depending on aid from us, and an attack on our compound is another challenge that we can do without."

Mr. Ban, a diplomat who usually speaks in carefully crafted statements, issued his strongest statement to date on the conflict, which mushroomed on Dec. 27 after a six-month cease-fire expired and Hamas resumed rocket fire at Israel.

"I conveyed my strong protest and outrage to the defense minister and the foreign minister and demanded a full explanation," said Ban, who had met Ms. Livni earlier Thursday as part of a multi-national effort to bring the devastating 20-day-old war to an end.

Ban said in a press conference that he spoken to Barak. "The defense minister said to me it was a grave mistake and he took it very seriously," Ban said. "He assured me that extra attention will be paid to UN facilities and staff and this will not be repeated."

In Gaza, flames from the bombings Thursday also engulfed the al-Quds Hospital in Gaza City, though it was unclear whether this was from a direct hit or from a fire resulting from a nearby attack.

A UN spokesman said that the headquarters was hit by what was believed to be three white phosphorous shells, which burn at higher-than-usual temperatures, and that UN workers were unable to douse the flames with standard fire extinguishers.

Thursday marked the second time since the war began that a UN facility took a direct hit from Israel.

Last week, Israeli forces bombed a UN-run school in Jabalya, in northern Gaza, killing 39 Palestinians sheltering there. The Israeli army says it hit the school because it was the source of mortar fire, but the UN says that no militants were found at the site.

At press time, emergency services in Beersheba, Israel, were dealing with the aftermath rocket attack there.

One of the Qassams launched by Hamas made a direct hit on a car. In all, Gaza militants fired at least 24 rockets at Israel Thursday, hitting cities such as Gedera, Ofakim, and Sderot. The wail of sirens, sending people in and out of bomb shelters, was heard throughout the day.