GAZA CITY, Gaza - Israeli mortar shells exploded Tuesday near a UN school in Gaza that was sheltering hundreds of people displaced by Israel's onslaught against Hamas militants, killing at least 30 Palestinians, tearing bodies apart and staining streets with blood.
Israel's military said its shelling -- the deadliest single episode since Israeli ground forces invaded Gaza Saturday -- was a response to mortar fire from within the school and said Hamas militants were using civilians as cover.
Two residents of the area who spoke by telephone said they saw a small group of militants firing mortar rounds from a street near the school, where 350 people had gathered to get away from the shelling. They spoke on condition of anonymity for fear of reprisal.
Majed Hamdan, an AP photographer, rushed to the scene shortly after the attacks. At the hospital, he said, many children were among the dead.
"I saw women and men -- parents -- slapping their faces in grief, screaming, some of them collapsed to the floor. They knew their children were dead," he said. "In the morgue, most of the killed appeared to be children. In the hospital, there wasn't enough space for the wounded."
He said there appeared to be marks on the pavement of five separate explosions in area of the school.
An Israeli defence official, speaking on condition of anonymity because he was not allowed to make the information public, said it appeared that the military used 120mm shells, among the largest mortar rounds.
UN officials demanded an investigation of the shelling. The carnage, which included 55 wounded, added to a surging civilian toll and drew mounting international pressure for Israel to end the offensive against Hamas.
President-elect Barack Obama broke his silence on the crisis Tuesday saying, "the loss of civilian life in Gaza and in Israel is a source of deep concern for me." He declined to go further reiterating his stance that the United States has only one president at a time.
At the UN in New York, Secretary General Ban Ki-moon called the Israeli bombardment of the group's facilities in Gaza "totally unacceptable." Israel's shells have fallen around three schools, including the girls school hit Tuesday, and a health centre for Palestinian refugees.
Some 15,000 Palestinians have packed the UN's 23 Gaza schools because their homes were destroyed or to flee the violence. The UN provided the Israeli military with GPS co-ordinates for all of them.
U.S. Secretary of State Condoleezza Rice met Tuesday with Palestinian President Mahmoud Abbas to lobby for a U.S.-backed ceasefire plan for Gaza.
Arab countries were floating a revised UN resolution calling for an immediate end to all military action, and deployment of an international observer force to monitor a ceasefire and protect Palestinian civilians in Gaza.
In the wake of the criticism, Israel agreed to set up a "humanitarian corridor" to ship vital supplies to the Gaza Strip, an idea that had been floated by the UN Security Council. Under the plan, Israel will suspend attacks in certain areas to allow people to get supplies.
The three mortar shells that crashed down on the perimeter of the UN school struck at mid-afternoon, when many people in the densely populated camp were outside getting some fresh air, thinking an area around a school was safe.
Images recorded by a cameraman from AP Television News showed crowds fleeing the scene, pavements smeared with blood and battered bodies of the dead being carried off by medics and horrified bystanders.
A youth who limped away from the scene was helped along by several others. Sandals were scattered on the pavement by a pock-marked wall.
World powers that tried but failed to get a truce in place before Israel sent in its ground forces warned of the potential for higher civilian casualties if the fighting moved onto Gaza's streets, and Gaza's main hospital has been overwhelmed with wounded innocents.
Mortar fire, in particular, is far less accurate than the laser-guided bombs Israel has used throughout the campaign.
The UN agency that runs the school along with other programs for Palestinian refugees said two other UN schools in Gaza were struck by Israeli fire since Monday night.
In the first incident, an air strike on the Asma Elementary School in Gaza City killed three men who were among more than 400 people taking refuge in the building. In the other, an artillery shell landed inside an empty boys school in Jebaliya.
"There's nowhere safe in Gaza. Everyone here is terrorized and traumatized," said John Ging, head of Gaza operations for the United Nations Relief and Works Agency.
The episode is certain to add to the urgency of truce efforts by leaders from Europe and the Middle East.
"I sincerely hope that for the sake of those who have died that it will not have been in vain, that it will spur everybody into more immediate action to get this ceasefire agreed and just stop horrific violence," Ging said.
An Israeli military statement said it received intelligence that the dead at the girls school included Hamas operatives, among them members of a rocket launching cell. It identified two of them as Imad Abu Askar and Hassan Abu Askar.
Two residents who spoke to an AP reporter by phone said the two brothers were known to be low-level Hamas militants. They said a group of militants -- one of them said four -- were firing mortar shells from near the school.
An Israeli shell targeted the men, but missed and they fled, the witnesses said, refusing to allow their names to be published because they feared for their safety. Then another three shells landed nearby, exploding among civilians, they said.
Palestinian militants have frequently fired from residential areas in the past.
Ging said the UN agency's staff work to prevent militants from entering the schools it has opened to shelter those at risk.
"Unfortunately tonight's incident is just another example of how Hamas operates," said Israeli government spokesman Mark Regev. "This is not the first time they have exploited a UN facility. This is not the first time that they have deliberately used innocent civilians as human shields."
A total of 71 Palestinians were killed Tuesday, with just two confirmed as militants, health officials in Gaza said.
Dr. Bassam Abu Warda, director of Kamal Adwan Hospital, said 36 people were killed, while the United Nations confirmed 30 deaths.
Israeli TV news broadcasts gave most of their attention to continued rocket fire on southern Israel. One of the two dozen rockets fired from Gaza on Tuesday wounded an Israeli infant.
There seemed to be little preoccupation in Israel with the deadly scene at the school.
In the past, however, Israeli ground offensives have been cut short when an errant shell or missile hit a civilian centre, killing and wounding women and children, leading to an international outcry that forced Israel to stand down.
Seven Israeli soldiers have been killed since the ground operation began, including four killed Monday in a two separate friendly fire incidents. Higher tolls among soldiers could also sap support for the offensive.
Despite international criticism over civilian deaths and calls for a ceasefire, Israeli tanks rumbled closer to the towns of Khan Younis and Dir el Balah in south and central Gaza but were still several kilometres outside, witnesses said. Israel already has encircled Gaza City, the area's biggest city.
Venezuela's government expelled the Israeli ambassador and embassy personnel because of the assault as a high-level European Union delegation met with President Shimon Peres Tuesday in a futile bid to end the violence.
Commissioner Benita Ferraro-Waldner acknowledged Israel's right to self-defence, but said its response was disproportionate.
"We have come to Israel in order to advance the initiative for a humanitarian ceasefire and I will tell you, Mr. President, that you have a serious problem with international advocacy, and that Israel's image is being destroyed," she said, according to a statement from Peres' office.
